Not announcing your firearm while trying to take cover
There have been many times that I have been at the range and was downrange changing targets and could look back and see the firearms on the table. I remember hearing about all of those sniper and counter sniper stories about seeing the flash of a rifle scope and knowing exactly where your opponent was. It really is that obvisous when you are on the opposite end of a rifle and the sun is behind you but there are also may modern acccessories that don’t help you keep a low profile. Trijicon sells the flash kill device for then end of an ACOG and they are very important is sunny places like Iraq. As soon as you look out the window with your firearm you can announce your presence from hundreds of yards away if you do not use a flash kill.
Many flashlights also give you away and having a red lense over the end of your light or anything other than the white reflective mirrors can help. There are other things you can do by even using different color magpul pmags other than Black. Black magazines can cover you in darkness but in certain urban environments foliage green or flat dark earth might be a better magazine to use. Mixing up your rifle stock colors or even painting it to match it’s environment can help give you a better chance at using concealment.