Re: Signature on tx messages
The default message app doesn't give you any option to auto add signature into messages. However, the work around that I can think of is that you go to settings> general> keyboard> text replacement/ there i can enter let say "SAB" to correspond to my signature as Ariel Babalao.
Now each time I type an SMS, at the end of it, I just need to type SAB, and it will convey it automatically to my signature.
Hope that help until perhaps, Apple provide a proper way.