When a folder has restrictions it is shown with a 'key' icon next to the title rather than the normal 'folder' icon (see 'Complaints' Folder below).
If you want to see who has access to this folder (assuming you do otherwise you will not see it!) then click on the folder name and then click on the 'Restricted' link under the title (see example below). If you want to see which users are in the group that is being used to set the restriction then go to Users/Groups and click on the relevant group.
If the folder is a sub-folder of a restricted folder then it is the top level parent folder that will display the restrictions.