I actually play that game quite often. When I'm in the subway, there's tons of youg people coming out of their schools and such, and I often come across a guy or gal and I'm like "I bet he/she watches anime", and I then start looking for stuff that tells the tale, and sure enough, several times I've found a keychain figure in their backpack, or some buttons, a t-shirt, necklaces with anime motifs (coolest one of the bunch was a Gurren Lagan drill), or when they finally step in the train and the doors close, they pop out a manga off their backpacks and such. So it works!
Never talked to any one of them, though. Only with that Sailor Moon girlie I talked you guys about at ARM.