Some of my colleagues list all their degrees in their signature line . . . . I'm an English instructor working for a U.S. university overseas . . .
Listing your degrees in your email signature is extremely uncommon in the U.S. and makes you look like a tool. I wonder though if it is not more common at institutions such as yours, where American degrees and doctorates are perhaps less common? In any case, go with the local culture.
Interesting...this is different in my discipline, where I don't think I've seen an e-mail signature file that
doesn't list degrees and relevant professional certifications. Of course, that could just mean that everyone in my discipline is a tool.
In my field (and university), the norm is something like this:
Jane Doe, PhD
Associate Professor
regular contact info
or Jane Doe, PhD CPA
Jill Gates Professor of Accounting
regular contact info
I think these are untenured's second option, perhaps?
No other degrees are ever listed, even if the sender doesn't have a PhD. CPA is listed though, if one is a CPA, even if one doesn't have a PhD.
This may not apply in your field, of course.
I'd go with the "do what is normal in your neck of the woods" advice.