diff --git a/includes/controller/shifts_controller.php b/includes/controller/shifts_controller.php
index 126678a7..90753217 100644
--- a/includes/controller/shifts_controller.php
+++ b/includes/controller/shifts_controller.php
@@ -41,11 +41,20 @@ function shift_controller() {
   if ($angeltypes === false)
     engelsystem_error('Unable to load angeltypes.');
   
-  User_angeltypes($user);
+  $user_shifts = Shifts_by_user($user);
+  if ($user_shifts === false)
+    engelsystem_error('Unable to load users shifts.');
+  
+  $signed_up = false;
+  foreach ($user_shifts as $user_shift)
+    if ($user_shift['SID'] == $shift['SID']) {
+      $signed_up = true;
+      break;
+    }
   
   return [
       $shift['name'],
-      Shift_view($shift, $shifttype, $room, in_array('admin_shifts', $privileges), $angeltypes, in_array('user_shifts_admin', $privileges), in_array('admin_rooms', $privileges), in_array('shifttypes', $privileges)) 
+      Shift_view($shift, $shifttype, $room, in_array('admin_shifts', $privileges), $angeltypes, in_array('user_shifts_admin', $privileges), in_array('admin_rooms', $privileges), in_array('shifttypes', $privileges), $user_shifts, $signed_up) 
   ];
 }
 
diff --git a/includes/model/Shifts_model.php b/includes/model/Shifts_model.php
index ee9c3773..37c772bf 100644
--- a/includes/model/Shifts_model.php
+++ b/includes/model/Shifts_model.php
@@ -1,5 +1,74 @@
 <?php
 
+/**
+ * Check if a shift collides with other shifts (in time).
+ * @param Shift $shift
+ * @param array<Shift> $shifts
+ */
+function Shift_collides($shift, $shifts) {
+  foreach ($shifts as $other_shift)
+    if ($shift['SID'] != $other_shift['SID'])
+      if (! ($shift['start'] >= $other_shift['end'] || $shift['end'] <= $other_shift['start']))
+        return true;
+  return false;
+}
+
+/**
+ * Check if an angel can sign up for given shift.
+ *
+ * @param Shift $shift          
+ * @param AngelType $angeltype          
+ * @param array<Shift> $user_shifts          
+ */
+function Shift_signup_allowed($shift, $angeltype, $user_angeltype = null, $user_shifts = null) {
+  global $user, $privileges;
+  
+  if ($user_shifts == null) {
+    $user_shifts = Shifts_by_user($user);
+    if ($user_shifts === false)
+      engelsystem_error('Unable to load users shifts.');
+  }
+  
+  $collides = Shift_collides($shift, $user_shifts);
+  
+  if ($user_angeltype == null) {
+    $user_angeltype = UserAngelType_by_User_and_AngelType($user, $angeltype);
+    if ($user_angeltype === false)
+      engelsystem_error('Unable to load user angeltype.');
+  }
+  
+  $signed_up = false;
+  foreach ($user_shifts as $user_shift)
+    if ($user_shift['SID'] == $shift['SID']) {
+      $signed_up = true;
+      break;
+    }
+    
+    // is the shift still running or alternatively is the user shift admin?
+  $user_may_join_shift = true;
+  
+  // you cannot join if user alread joined a parallel or this shift
+  $user_may_join_shift &= ! $collides;
+  
+  // you cannot join if you already singed up for this shift
+  $user_may_join_shift &= ! $signed_up;
+  
+  // you cannot join if user is not of this angel type
+  $user_may_join_shift &= $user_angeltype != null;
+  
+  // you cannot join if you are not confirmed
+  if ($angeltype['restricted'] == 1 && $user_angeltype != null)
+    $user_may_join_shift &= isset($user_angeltype['confirm_user_id']);
+    
+    // you can only join if the shift is in future
+  $user_may_join_shift &= time() < $shift['start'];
+  
+  // User shift admins may join anybody in every shift
+  $user_may_join_shift |= in_array('user_shifts_admin', $privileges);
+  
+  return $user_may_join_shift;
+}
+
 /**
  * Delete a shift by its external id.
  */
diff --git a/includes/pages/user_shifts.php b/includes/pages/user_shifts.php
index a727bbcb..603ca993 100644
--- a/includes/pages/user_shifts.php
+++ b/includes/pages/user_shifts.php
@@ -9,8 +9,8 @@ function user_shifts() {
   
   if (User_is_freeloader($user))
     redirect(page_link_to('user_myshifts'));
-
-  // Locations laden
+    
+    // Locations laden
   $rooms = sql_select("SELECT * FROM `Room` WHERE `show`='Y' ORDER BY `Name`");
   $room_array = array();
   foreach ($rooms as $room)
@@ -62,8 +62,8 @@ function user_shifts() {
     if (count($shift) == 0)
       redirect(page_link_to('user_shifts'));
     $shift = $shift[0];
-      
-      // Engeltypen laden
+    
+    // Engeltypen laden
     $types = sql_select("SELECT * FROM `AngelTypes` ORDER BY `name`");
     $angel_types = array();
     $needed_angel_types = array();
@@ -543,14 +543,16 @@ function view_user_shifts() {
                 
                 // qqqqqq
               $is_free = false;
-              $shifts_row = date('d.m. H:i', $shift['start']);
+              $shifts_row = '<a href="' . shift_link($shift) . '">' . date('d.m. H:i', $shift['start']);
               $shifts_row .= " &ndash; ";
               $shifts_row .= date('H:i', $shift['end']);
               $shifts_row .= "<br /><b>";
-              $shifts_row .= '<a href="' . shift_link($shift) . '">' . ShiftType($shift['shifttype_id'])['name'] . '</a>';
+              $shifts_row .= ShiftType($shift['shifttype_id'])['name'];
               $shifts_row .= "</b><br />";
-              $shifts_row .= '<a href="' . shift_link($shift) . '">' . $shift['title'] . '</a>';
-              $shifts_row .= "<br />";
+              if ($shift['title'] != '') {
+                $shifts_row .= $shift['title'];
+                $shifts_row .= "<br />";
+              }
               if (in_array('admin_shifts', $privileges))
                 $shifts_row .= ' ' . table_buttons(array(
                     button(page_link_to('user_shifts') . '&edit_shift=' . $shift['SID'], glyph('edit'), 'btn-xs'),
diff --git a/includes/view/Shifts_view.php b/includes/view/Shifts_view.php
index 594cb33c..00c18572 100644
--- a/includes/view/Shifts_view.php
+++ b/includes/view/Shifts_view.php
@@ -1,6 +1,23 @@
 <?php
 
-function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source, $user_shift_admin, $admin_rooms, $admin_shifttypes) {
+function Shift_signup_button_render($shift, $angeltype, $user_angeltype = null, $user_shifts = null) {
+  global $user;
+  
+  if ($user_angeltype == null) {
+    $user_angeltype = UserAngelType_by_User_and_AngelType($user, $angeltype);
+    if ($user_angeltype === false)
+      engelsystem_error('Unable to load user angeltype.');
+  }
+  
+  if (Shift_signup_allowed($shift, $angeltype, $user_angeltype, $user_shifts))
+    return button(page_link_to('user_shifts') . '&shift_id=' . $shift['SID'] . '&type_id=' . $angeltype['id'], _('Sign up'));
+  elseif ($user_angeltype == null)
+    return button(page_link_to('angeltypes') . '&action=view&angeltype_id=' . $angeltype['id'], sprintf('Become %s', $angeltype['name']));
+  else
+    return '';
+}
+
+function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source, $user_shift_admin, $admin_rooms, $admin_shifttypes, $user_shifts, $signed_up) {
   $parsedown = new Parsedown();
   
   $angeltypes = [];
@@ -15,7 +32,9 @@ function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source,
     if ($needed_angeltype['taken'] >= $needed_angeltype['count'])
       $class = 'progress-bar-success';
     $needed_angels .= '<div class="list-group-item">';
-    $needed_angels .= '<div class="pull-right">' . button(page_link_to('user_shifts') . '&shift_id=' . $shift['SID'] . '&type_id=' . $needed_angeltype['TID'], _('Sign up')) . '</div>';
+    
+    $needed_angels .= '<div class="pull-right">' . Shift_signup_button_render($shift, $angeltypes[$needed_angeltype['TID']]) . '</div>';
+    
     $needed_angels .= '<h3>' . AngelType_name_render($angeltypes[$needed_angeltype['TID']]) . '</h3>';
     $needed_angels .= progress_bar(0, $needed_angeltype['count'], $needed_angeltype['taken'], $class, $needed_angeltype['taken'] . ' / ' . $needed_angeltype['count']);
     
@@ -42,6 +61,8 @@ function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source,
   
   return page_with_title($shift['name'] . ' <small class="moment-countdown" data-timestamp="' . $shift['start'] . '">%c</small>', [
       msg(),
+      Shift_collides($shift, $user_shifts) ? info(_('This shift collides with one of your shifts.'), true) : '',
+      $signed_up ? info(_('You are signed up for this shift.'), true) : '',
       ($shift_admin || $admin_shifttypes || $admin_rooms) ? buttons([
           $shift_admin ? button(shift_edit_link($shift), glyph('pencil') . _('edit')) : '',
           $shift_admin ? button(shift_delete_link($shift), glyph('trash') . _('delete')) : '',
@@ -55,7 +76,7 @@ function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source,
           ]),
           div('col-sm-3 col-xs-6', [
               '<h4>' . _('Start') . '</h4>',
-              '<p class="lead">',
+              '<p class="lead' . (time() >= $shift['start'] ? ' text-success' : '') . '">',
               glyph('calendar') . date('y-m-d', $shift['start']),
               '<br />',
               glyph('time') . date('H:i', $shift['start']),
@@ -63,7 +84,7 @@ function Shift_view($shift, $shifttype, $room, $shift_admin, $angeltypes_source,
           ]),
           div('col-sm-3 col-xs-6', [
               '<h4>' . _('End') . '</h4>',
-              '<p class="lead">',
+              '<p class="lead' . (time() >= $shift['end'] ? ' text-success' : '') . '">',
               glyph('calendar') . date('y-m-d', $shift['end']),
               '<br />',
               glyph('time') . date('H:i', $shift['end']),