I carry my extra mag owb right behind my holstered flashlight. The flashlight sticks out farther than the mag, and, not that it has occurred yet, I can playoff the extra mag with a "That's my flashlight." statement unless it is fully visible. Even then, I think it would take most people a few minutes at least to realize what they saw. Recent experience has taught me how clueless the general, unknowing public is when it comes to spotting a concealed carry. I've carried a Glock 20 owb under nothing but a Columbia PFG shirt around friends who would definitely call me out if they had seen it. I've carried my normal 26 iwb numerous times under nothing but a t-shirt around those same people without any clue from them. I've received lots of hugs while carrying with no discovery. I have been asked if I was carrying a couple of times but not because there was any sign of it. The first, 19 iwb, was a random joke that about gave me a heart attack because I was admittedly carrying in a questionable location surrounded by cops. I very carefully pulled my shirt up as far as possible and gave myself a patdown to calm the guy sitting next to me; he accepted that I didn't have one. The second time, 26 iwb, it was just me and a liberal northern Illinois girl (see hugs above) who I was trying to give a lesson in guns aren't evil. We were at her place, and I was going to let her hold one of mine. She thought I had to go home to get it. When I said it was closer than that, she asked if I had one on me. I didn't specifically answer that question but said I had to get it out of the truck which was true for the one I was going to get. She didn't know. Both times, I had a spare mag on the other side along with my flashlight. I've even had one of my trusted friends (a ccw holder who changed states and can't carry for now) who knows I carry admit to regularly looking for it without success. He said he's thought he saw it a couple of times only to realize it's my flashlight. I thanked him for looking and asked him to tell me in private if he ever does see it. I want to know if it's not working. Not that it's ever a good idea to take the concealed aspect too lackadaisically, I don't think it's too hard to actually conceal a pistol even when you can see it on you in every reflection. The exception is like this example where a knowledgeable concealed carrier spots it and knows.
I know laws vary, but is there any case where an exposed spare mag would actually be considered a crime?