Sometimes they have a clip like these do and sometimes they have a little wire spiral that you would slip a photo in to display it.
Well I picked these up at a wonderful stationery store that I sometimes do trunk shows at and I have gotten so much use out of them.
I have used them for price signs, to hold a small bio card about me, to hold sale signs, to display a business card, to hold an information sign about a particular product...etc...
They are small and light...which is a MUST for packing and transport.
Next time you are out and about...keep your eyes open. I have even seen cute themed ones at the dollar store!