I "think" you are asking how to remove a signature that you added? You don't mention what device, what Android version, or what texting app, so I can only answer in general terms. Open you text app and access its Settings menu. For example, on my S4, I have two textings apps (the stock Samsung one, + HeyWire). In both cases Settings is accessed by pressing the' Menu' soft-key from within the app. In the stock app, it's Settings > Add signature; in HeyWire, it's Settings > Signature. It should be something similar on your phone.