Actually they do tell you. If you go to the Sun Poker page on
rakeback, you will see the US flag with a big red X over it. And a lot of the pictures have a small US flag on the bottom right if they allow US players. If those two huge things don't give you a hint wether or not that poker room takes US player, reading the fine print on ANYTHING you ever register for is usually a good idea. Wouldn't wanna get scammed...