I don't think you can get it to leave a signature. The only way you could make it easy is by going to autotext in options, and make a signature on that. example: you can make it so when you type "sig" in the sms/email/bbm that it will change to the phrase you want to be a signature. I use autotext alot. I made it change "u" to "you and "idk" to "i don't know" it's helpful