While I love the Blank Canvas signature there is an alternative until the addon is fixed.

Go to Settings > Labs in your gmail account.

Enable "Canned Responses"

Enable "Inserting Images"

Compose a new e-mail write in your signature as you would like it to appear. Insert any images you may like. From the Canned Responses menu select "Save Canned Response".

Please remember this does not automatically populate your signature. You need to select it from the canned responses menu.