Like it or not, Gmail just brought your desktop signature to mobile
If you have set your signature to show up for new emails and/or replies, Gmail will automatically add them on the web and ...
Android Authority19d
The Gmail app is getting a quality-of-life upgrade you didn't know you needed until now
The Gmail app on Android can now use your signature on desktop. If you don’t have a separate signature setup on mobile, the app will use your web signature for replies and new messages.