I see the people running out and slapping all sorts of stickers (firearms related and not) on their vehicles, and then they look dumbfounded when I tell them that makes them a prime target. With a bit more of a stretch, the US MIL plates that recently came out are another perfect example. Should there be a "lone wolf" attack, easily recognizable license plates are a perfect indicator of targets to remove, as current and former MIL will most likely provide the most resistance.
Regarding the "gray man", sometimes it is beneficial to be unremarkable. Medium height, medium weight, medium build. Blue jeans, boots or sneakers, and a plain T-shirt. Jackets are usually black or gray. Takes next to nothing to remain unremarkable. You can be in the best shape of your life, and by adding even a slight stoop to your shoulders and back can reduce your overall height by up to 3", and reduce your potential "threat projection" by quite a bit.