I see that JeffG7BRJ gave us an interesting puzzle. 

I see that TwoPynts gave a quick response that,

It is a button!

I wouldn't think so ... it doesn't have holes for the thread. 

It doesn't seem the right color for a coin. 

It could be a chocolate coin ... but since one of the hints was that everybody on renderosity has one ... that might be a guess ... but wouldn't be my best guess. 

On my Canon A1 film camera, the rewind knob is also the ASA setting adjustment and does have a similar knurled edge ... but that would have the film rewind knob/lever showing. 

IOW, good challenge, thanks ... I need to rest and think ... more ...

--
Martin