the symbol that most people use for checkmate is #.
A few things to read before you want to post your first forums.

WTH! means "with those heels". As in: "Look at those shoes! WTH!"
WTF? means "why trade farms?". As in: "His farm is run down, compared to yours. WTF?"
To post a forum,click on http://www.chess.com/forum/post.html?cat_id=10 to post your own forums.
The following is something you should read it carefully,send some replies for help about the article below:
To all forum poster:
Welcome to post your 1st forum(or you are not the 1st time).The following symbols will help you.
+ check
++ double check(some means checkmate)
... Black's move
! good move
!! <continued>