Bingo! People are far more likely to be "made" as a result of their actions (especially constantly checking the weapon for concealment, etc.) than because of the gun "printing."What draws MY attention is people touching the gun thru the clothing. Many people do this with realizing it. I also notice unusual activity and body movements, like a guy holding his jacket/vest/shirt down with one hand while digging for his wallet with the other....
There are some more subtle ways to spot people who are likely carrying. I've started looking for people who are obviously carrying their cell-phones on their weak-hand side. ;)