M.S.
Next time they do that, look them dead in the eye and do not smile, laugh or anything. Tell them stop, its not funny and I would appreciate if you don't make fun of me. If they continue then you need to tell HR dept. but hopefully by you letting them know that its not funny, they will stop. Its hard to tell without the history, if they are the type to be doing it for fun or if they really have a problem with you. Either way---try not to let it bother you and address it with them first before going to a supervisor. Good luck!
Molly