Open the message application, press menu then settings.. look in the Storage option. Check box that says Auto add signature. It will ask you to enter text as signature ... at least that is where it's at on the Verizon model.
If not on ATT then download GO SMS it has the signature option
Sent from my VS980 4G using XDA Premium HD app
LG G2 (In Use)
I called Google Device Support the other day, and asked about the possibility of Modem/Radio within the Nexus 7 3G.. and The CSR answer was "No you can not plug a Phone Cord or Ethernet cable into the device, and if you want to listen to the radio you must download a 3rd Party App or Try our Google Music service, but it's not a radio" - Couldn't help but laugh uncontrollably for 10min straight. ~UberSlackr