You will have to download Handcent for you to add a signature in the Samsung Galaxy precedent. Open the handcet after you have downloaded it and yap 'Menu'. Secondly, press for settings and then step scroll down to select 'Send message' settings. Next, check the 'Enable signature box' and tap 'Personal signature'. Finally, you will type in the text that you want to use as your text message signature and click OK.