Currently I have an HTML signature for my work account on Thunderbird desktop that contains some simple text formatting and a logo image, but pasting the same HTML into the signature setting in K-9 Mail just inserts the HTML as text into the email.
Wonderful idea! I would suggest it myself since i just experienced this problem. It is my great wish to use a signature on my mobile. I use thunderbird on my phone for work. I aint always able to get back behind my PC to send professional e-mails, when i'm on the road. I hope it will be able to use this feature soon, since i really would experience more ease sending my business e-mails with a professional signature, banner and my professional lay-out when i am on the road for a longer period of time and not able to use a PC. The idea of being able to use this makes me really enthousiastic! 😄