Martin Koistinen has posted some tips on how to manage signatures in Thunderbird.
He offers some code 
for a CSS signature. It follows the same principles as CCS signatures for Mail.app posted here in the past, but with all the bells and whistles you could ever want.
It won’t appeal to everyone, but people who have made their peace with HTML in email will be delighted at how comprehensive the code is:
Not content with that, he has also created a randomiser for Thunderbird sigs. The shell script he provides will insert a tag line from a user-created list into this CSS signature or any HTML signature file. Full instructions in the post make it easy to craft your own. Nice.
I hope I will never get such a signatures from anyone. It is just waste of space.
I might be conservative but I think email should be text only, no HTML and no CSS. There is really no need for it.
I find this signature very original, expressing in different way all the boring information that we put anyway.
Like this at least we can enjoy for a minute the end of our emails.
Have a bit more imagination and instead of “waste of space” make it “use of space”!
I think those signatures are useless anyway. VCards as an MIME attachment can imported directly into the address book.
Besides I think a CSS designed signature will look not only funny if you just wrote a single line.
I think people need to get over this “email should be plain text” crap. It’s the 21st Century. Join us, already. The water’s fine.
[...] Hawk Wings » Blog Archive » Thunderbird: CSS signatures, random signatures It won’t appeal to everyone, but people who have made their peace with HTML in email will be delighted at how comprehensive the code is (tags: thunderbird extensions) [...]
I have used the above mentioned example with Thunderbird and everything I send an email the other person getting the mail is also getting 5-6 image attachments, even though I check send and text and html.
How are you sending mail with Thunderbird and preventing Thunderbird from stripping it and adding everything as an attachment?
Jonathan — Rather than lead you astray with some ill-informed comment on how Thunderbird works, I wonder whether you might be better off getting in touch with Martin Koistinen who wrote the original code?
http://mkoistinen.googlepages.com/css-signatures
He is much more likely to know what he is talking about than I am,