Best way to spot them is looking at the sides, just like you look for silver. Proof coins will appear just a tad wider than the rest, and will have crisper, sharper edges on the rim. Any that you see looking like this, go ahead and check the Mint mark to be sure.
Well I have to admit I don't search other denominations much and am not for sure. I do know that a S mint mark on a nickel does not mean it is a proof as in halves. Found that out when I posted one here and was excited I had found a proof nickel! ha, ha Was told at least the one I had found was not a proof
Good Hunting!!!!!!!
I think there was a point at which the San Fran mint stopped producing business strikes and only struck proofs, which would mean that after that date all S mint coins are proof, but I don't know what that date is. Plus I don't know how to ID older coins when the san fran mint WAS producing business strikes.