If you are having trouble getting your sig to show up then go in your profile, go to prefrences and look for "Always attach my signature :" and make sure that YES is selected.

If that didn't work

When you are posting a message there is a box at the bottom of the page that says options (this may be collapesed, if so you need to hit the + sign on the right side of the bar) in this box you need to make sure that the box beside "Attach my signature" is checked.

Any more problems just let me know