If you really want a sig, you could create a keyboard shortcut. Just remember that a sig uses part of the 160 character limit per SMS.
"If you want to do something big in your life, you must remember that shyness is only the mind. If you think shy, you act shy. If you think confident you act confident. Therefore never let shyness conquer your mind."
- Arfa Karim, Microsoft's youngest certified professional, 2005 at the age of 9.
She died in 2012 at the age of 16.