You can't, automatically, for SMS text messages (hence the name SMS = Short Message Service).
You can add a signature each time, using AutoText, as described above. I have one where I type 'ZX' and my name, email and cell # are entered.
For your email, set your BIS signature: How do I edit the "Sent from my BlackBerryÂ®..." message? - BlackBerryFAQ