- Good skintone/facial recognition software on your hidden webcam
- Be one of the participants. You'll usually notice.
- Apartment living. Your neighbors will not fail to alert you.
- When the creepy dude who worked nights at the local video store, who just filled the tank of his 70s station wagon and picked up cigarettes and condoms, runs back into the gas-mart an hour later – comb-over flying wildly about – and asks if you sell "D size batteries"[*].
- If they mention it overly-loudly to their friend on the other end of the phone while in line behind you at the DMV.
- if you ask them, and they say "yes".
[* No, that's not a funny joke, but a part of my memory I cannot erase. ]