I had a similar chat with some people on these boards a few months ago. In preparing for my first cruise in August, I was under the impression that it had to have a raised seal.
However, it was pointed out by some that each state might handle it differently. The example offered was South Carolina that apparently issues a wallet size B.C. that does not have a seal.
The key message others pointed to was weather or not it indicated "Official" somewhere on the certificate.
My advise, depending on when you are going, take the time to check with your state's Office of Vital Statistics. Worst case, go to the state's website and order a new one - then you can be certain. I ordered new ones for both my wife and I, and it cost me $10 each. One was from Delaware the other Pennsylvania - so I think the $10 is fairly standard.
In fact, if you are OK with purchasing online, you can go to: