Tracers Work Both Ways

http://m-joke.8m.com/murphys.htm

Some of the more successful fighter pilots of WW2 did not load tracer rounds. The tracers in a close shot would alert the enemy. Without the tracers, the enemy didn't know he was being shot at, giving the attacker another shot (yes, many WW2 dogfights happened without the victim ever having seen the attacker).