A great way to encourage more ubiquitous email encryption is to let people you’re emailing know that you’re equipped to use it, and that they can be too.
Some people use PGP signatures for that purpose, but inline signatures can be off-putting to people who don’t know what they are, and attachments can be similarly confusing. (Not to mention that, as XKCD notes, the security benefits are pretty slim.)
A one-line addition to an email signature is a good compromise. I propose the following:
I prefer to use encrypted email. My public key fingerprint is 4FF3 AA1B D29E 1638 32DE C765 9433 5F88 9A36 7709. Learn how to encrypt your email with the Email Self Defense guide.
In my case, because I’ve got my key available on an HTTPS site, I’d probably link to it directly as well.
This system isn’t perfect, and in particular is not a very secure way to distribute your fingerprint. But it could be a good nudge to people who might be considering learning about email encryption while flagging you as somebody who might be able to help, and especially if you post to publicly archived mailing lists, it’s a way of getting your fingerprint tied to your emails in lots of places.