We're excited to introduce an updated and improved signature editing experience for our Insider Fast users starting in version 16.12 (180314).
As before, to open the signature editor, navigate to Outlook > Preferences > Signatures, and either create a new signature (by clicking on the + button) or edit an existing one (by clicking on the Edit button).
With this update you will now be presented with a larger compose window -- with a variety of formatting controls as well as the ability to insert images, links, and tables -- to help you fine tune your signature exactly to your liking! You can also add alt text to images directly in the editor.
We would love to hear from you as we make improvements in Insider Fast, so please provide feedback and report issues via Help > Contact Support. If you would like to see other enhancements in Outlook for Mac, please vote for your feature request via Help > Suggest a Feature.