Gmail‘s signatures have always been borderline boring because you can’t have anything fancy on it (unless you manually edit in on the actual message) as it only supports plain text. Thanks to the multitude of us that keep on asking for rich text signatures, Google has finally given us exactly that; Rich Text Signatures :). Give yourself a nice pat on the back.
Google announced the new feature in a blog post, and said that rich-text signatures had been one of the “most requested” features among Gmail users.
One caveat though, Mark Knichel, a Google software engineer says that only the latest desktop version of Gmail would support rich-text signatures. Older versions of Gmail, the simplified HTML version, and mobile Gmail, will continue to use plain text signatures.
source Gmail Blog