A couple of times when I've been out and about I've seen expats and wondered if they are Geoexpatters. Who hasn't, right?
A couple of ideas:
1.) Geoexpat apparel...who wouldn't wear a Geo hat or a T-shirt with say, "I got flamed on Geoexpat!"...or "Geoexpat...you know where the airport is!"....
2.) What about a secret signal? It doesn't have to be really obvious like...
....just a couple of tugs on your left earlobe....
So. I propose that 3 tugs on your left earlobe is the code. If you see an expat, give your left earlobe a tug 3 times.....if it's returned, voila, your instincts were correct!