Given the size of maps, when characters are prone it can be extremely hard to find them. This can make playing against snipers overly frustrating.
When a character (AI/player) is LOOKING THROUGH a scope there would be an occasional SMALL flash at their position which is visible at long distance.
Flash would be proportionally less bright with overcast conditions.
This would simulate sun/sky reflection. Even though moden sights are designed not to, it can still happen.
Would be SMALL so that an observer would have to be looking CLOSELY in the general area to see it.