In all seriousness, this has been asked repeatedly, and is in the Help and How to Forum, on the first page, I think.
Be that as it may, to set up a sig for SMS messages, you need to set up an autotext.
Options>Autotext>BB Key>New
set your autotext, say for instance, your initials, then fill in the "replace with" field with your signature.
When typing your text, type in the autotext (in this case, your initials) and hit "space". The BB will autofill your sig.
Hope that helped, and if you don't mind a piece of friendly advice, read through the Blackberry 101 and the Help and How To Forum. You will find that between the two, they will answer a lot of questions you will have when starting out with a new BB.
please forgive the testiness at the beginning of the post, sometimes have to catch myself after answering the same question a few times
Thanks for the quick response. Autotext is the chit. I've done a lot of reading on here and have taken in a lot since getting my BB. My first few days with it I wanted to take it back but told myself give it a few weeks. Well I'm sold. I love my BB to death. Wish I had gotten 1 a long time ago. Anyway, thanks for the help. It's much appreciated...
great tips everyone! I dont have a sig because like some already said, it uses your letter allowance. plus most peole you are txting already have you in there phone so they know who you are. I find them annoying when people txt me with a sig. But whatever floats your boat! enjoy!