Is it possible to code an HTML responsive signature for Gmail? I am trying use the media queries, but it's not working on the web client or Gmail Android App.
Thanks
It's but not with media queries.
The problem is that some e-mail clients stripe all <style>...</style> tags out. If I remember correctly, GMail is no exception.
So, yes, you can build responsive layout by using inline CSS with values in % but it will be completely responsive then. It is to say it will absolutely depend on the parent container size.
However, your e-mail signature will unlikely ever appear out of e-mail (which is the parent container), so, you just need to check that the signature looks nice at least in most popular screen sizes.