Make your mobile emails as professional as they are on a desktop.

HTML Signature lets you save your email signature and insert it in messages you're composing. Particularly for Android!

You can also subscribe to a premium version to save all kinds of text and HTML content to insert in to messages you're composing.
Save time on those paragraphs and phrases, or marketing content you otherwise end up re-typing time after time.

Available nearly everywhere you get Gmail - desktop, laptop, Android, iPhone
(not Tablets - Gmail doesn't support add-ons on tablets. You can "Star" the issue so it gets more attention from Google here: https://issuetracker.google.com/u/0/issues/150191145).