This article explains how to install Windows on an Android tablet. You can only add a text-based, nothing fancy signature. Maybe in the future, they will revert their decision but for now, HTML signature is not supported in Outlook for Android. Thanks for your understanding and keep letting us know your thoughts. We are still taking your votes and notes into consideration and we highly appreciate them: Sometimes we have to make decisions to improve the overall experience for the widest amount of people. We have a team spending their time on making sure our HTML rendering and message composition experiences are rich (formatting support is coming in the future).
We have had to make the decision that this isn’t something that we’re going to have on mobile.
However,although the request has more than 7 thousand votes, it was declined by Microsoft: Support HTML features in signature such as images and company logos as well as hyperlinks and formatting. There is a thread on UserVoice asking for: As of the wtiting of this answer (9 March 2019),Outlook for Android does not support HTML signature.