closes https://github.com/NodeBB/NodeBB/issues/4423

less/modules/taskbar.less

@@ -111,6 +111,10 @@
 					padding: 1px 2px;
 					font-family: @font-family-sans-serif;
 				}
+
+				&.new[data-content="0"]:after {
+					display: none;
+				}
 			}
 
 			&.taskbar-composer, &.taskbar-chat {

lib/persona.js

@@ -54,12 +54,20 @@ $(document).ready(function() {
 			}
 		});
 
+		socket.on('event:chats.markedAsRead', function(data) {
+			$('#taskbar [data-roomId="' + data.roomId + '"]')
+				.removeClass('new')
+				.attr('data-content', 0);
+		});
+
 		function createChatIcon(data) {
 			data.options.icon = 'fa-spinner fa-spin';
 
 			$.getJSON(config.relative_path + '/api/user/' + utils.slugify(data.options.title), function(user) {
 				var el = $('#taskbar [data-uuid="' + data.uuid + '"] a');
 				el.find('i').remove();
+				el.parent('[data-uuid]').attr('data-roomId', data.options.roomId);
+
 				if (user.picture) {
 					el.css('background-image', 'url(' + user.picture + ')');
 				} else {