Do you mean the owner's info for the lock screen? If so, it should be in the Lockscreen section of your Phone Settings.
If you mean a signature for texting or e-mail, that would depend on which app you're using. On the e-mail app, there's a Signature option in the e-mail app's settings. For texting, not sure the stock app supports signatures (wouldn't know why, when SMS are usually limited, any app would...)