Is there a way to add a signature to automatically show up in the text box in iMessage. I know that you could create a keyboard shortcut to type in everytime you text but there are two problems with that: every time you would use that shortcut normally (without the intentions of using the signature, the signature would come up), and I would need to put in the signature's shortcut every time I text.
I'm not sure it can be done automatically, but...
I'd just use the shortcut method.
I use 'mynm' to trigger mine - it's not something I'm likely to ever use for another purpose. Same for myeml myphone myaddy etc
Substitutions can even do emojis or multiple-line text with Return key - so long as you copy-paste them into the shortcut, not try to type them 'live'
You'll find it's easier, long-term, to type a few letters at the end of your message than fight it every time you don't want it to happen