Need ID help from playground

[OcdChaos]

Found this metal round thing at a playground. Small and pretty thin, very lightweight, smaller than thinner than a penny. It is concave on one side and convex on the other. Has a stamp in the center of the convex side, of a triangle with a H in the middle of the triangle. One of the pictures has it sitting on top of a penny for thickness and concaveness (made up word, ha) comparisons. Any thoughts? Thanks

 

[DannyB.]

Looks like the top half of a fastener.. a snap on children's clothing; possibly.

 

[mcl]

Am I nuts or does it sort of look like a "4" perched on top of the middle part of "H"? As in.. 4H?