It kind of started when I got this T-shirt as a present two years ago:

It is not just a slogan that is quickly filtered out under the heading 'generic ad-like content'. It invites checking where the error is. It is kind of a challenge - at least for suitably minded persons. Exactly that kind of person I'd like to get in touch with more. This T-shirt signals: "I'm a nerd and proud of it." And the positive feedback I got from this was part of the reason I chose to signal this more. Maybe you'd like to signal this too. Please remember the T-shirt alone will not do it. You still have to talk to people. For the introverted among us (me included) I recommend active listening.

The remainder of this post lists some slogans I have tried, some I will likely try shortly and other related resources.