Often, a member of staff will let you know when your Stint is finished. However, they may forget to do so if it's busy. Make sure you have spoken to the manager (or the person that has been assigned to look after you on your Stint) to let them know your Stint is over - never leave without saying anything.
After collecting your belongings, make sure to thank the Manager and other members of staff on the way out. Last impressions are almost as important as the first - leave with a smile and thank the staff for having you.