You can use signature for messages you send with your Android HTC One. Signature is shown at the bottom of all your messages. Add, Set signature on HTC One by doing as follows:
To set a signature for your Gmail account, see: How to Set a Gmail Signature on Android
1. Open "Messages"
2. Go to "Settings" by tapping the 3 dot icon on the top right
3. Tap "General"
4. Mark "Use Signature" to enable it. (You need to unmark this option to disable signature on HTC One)
5. Tap "Signature" to edit and write your signature. The default signature is: Sent from my HTC