Q: How do I put a my signature on a text ?

Hi. Do you mean the type of signature used by PDF files, or just a picture of a signature added to a document? Which app are you using to create the document?

If you mean a signature in a text message, there is no way to do that (and it's not commonly done). You can, if you want, use a Text Replacement shortcut to put something at the end of a text. Settings>General>Keyboard>Text Replacement.