#1. Space Bar (and alt + spacebar)
To jump to Top and Bottom, press T or B.
#2. Log into BIS via BlackBerry or PC and click edit email. Then add/edit sig line.
Setup
Email Settings
Log In
Highlight Email address
Menu
Edit
Signature
Also, if you don't want your email signature to be on every email sent, you can add an Auto Text that will put the signature in for you when you want it.
For example, if I push qqq, that changes to "Sent from my Sprint BlackBerry".