If you go to the bottom of any page in the SE network (e.g. this one!), you'll see a list of SE sites. In particular there's a link to MathOverflow, that is potentially seen by a large number of people (many of whom are outside of our target audience).
When you put your cursor over that link, there's a hover popup reading "mathematicians". If you try this with many of the other sites you'll find more a more detailed description.
We should improve this!
I'll provide a few samples as answers; please vote for the one you like, and we'll get it fixed.