Browsing the forums and I see alot of abbreviation and descriptions i don't understand. I'm trying to figure out what everything means on my own with sites posted here but i'm was looking on ebay and found few coins that I think are a good price (compared to some other coins I wanted to buy). The listing says "1992 S US Mint Silver Proof Coin Set in OGP + COA" what does OPG and COA mean? Not sure if I should buy this one. I get a penny, nickle, dime, quarter, and half dollar proof set for $25.99. Are they worth that much? Another listing says "Cameo proof" and "Deep Gem Cameo" not sure what that is.