A plain text email client won't necessarily show any images. Thunderbird would show it as an attachment. The email clients on this Android tablet often offer to fetch images on demand. So there is no guarantee that users will see an image. In theory you can use a naked image file as a signature, but I've never tried it, mainly because I've assumed that if I want to show an image, HTML is tacitly assumed. I use an addon that allows both a plain text signature and an HTML signature in the same file, the appropriate version being picked out according to the format of the message. Such an approach precludes images in plaintext messages. Speaking as a potential recipient, I don't like graphic only signatures. They look like attachments so generate clutter in the thread pane. They may fall foul of anti-virus and other security software. And I can't copy and paste info from them. If I wanted a signature in the sense of an penned autograph at the foot of a message, I know that to get it to appear in the right place I'd have to embed it and therefore would have to use HTML. You need to consider that anyone who sets their email client to show only plaintext, or chooses to use a text-only email client really doesn't want to see ''any'' graphics in their email. You're trying to cater for an audience who in reality don't want and don't care about your signature. I suspect that your other email clients work in HTML mode by default.