What is it used for?

You can put it in the Coin Machine in the Lower West Side of Centropolis for a prize. I think it's random what you get.

Ahh I see :) Thanks

in the old Forums, there was a thread in Games that had people post what they got. There may be a new thread now. I know that many of the Special Coins do stat boosting on your active pet, instead of any sP or prize. This is why they typically sell for more than what you could get from them by putting them in the Machine (but not always, I've gotten some nice stuff while attempting to boost)

Thanks for the info :)

Thanks for the info, I had been throwing the coins in my vault, not knowing what to do with them. I just spent three randomly, won some SP, one of my pets was filled with food and one went up a level :D