Possibly a "business card" or golf ball marker chip.

That reminds me of a poem.

"I had a little fish that went in and out with me
And what could be the use of him
Was more than I could see.

He followed me to school one day
Which was against the rules
But my teacher, Mr. Bear,
Thought he tasted really cool."

And a tip o' the hat to Rob Blooie Stevenson.