You can do all 5 steps in 2 seconds? Impressive.
1. From the Home screen, tap “Settings“.
2. Tap the “Mail, Contacts, Calendars” button.
3. Tap “Signature“.
4. Check the option to apply your signature to “All Accounts” or “Per Account“.
5. Change the Signature text from “Sent from my iPhone” to be blank or to whatever you like. If you selected “Per Account” in step 4, you may have to set the signature for several accounts such as Gmail, AOL, etc. as desired.
This post applies to Apple iOS 7.