Cannot by definition, be a war crime. These were not merely civilians directing traffic, but personnel loyal to Hamas, a hostile regime during a state of war; as such, they were a legitimate target for Israel. There is no reason to believe that they would not hesitate to either (A) engage Israeli troops directly or (B) report Israeli soldiers' presence and locations to Hamas command. They had to be targeted.
Suspect Bangkok bomber arrested, found with possible bomb-making materials (Reuters)
from the article: Hamas: Goldstone retreat doesn't negate war crimes committed in Gaza