When I was in the Army, one of my jobs was to activate smoke bomb canisters after our chopper landed on the ground. I had different colors of smoke, and the other chopper pilots would know what the conditions were like on the ground before they'd try to land. If they saw green smoke, they knew it was safe to land. If I pulled the red smoke bomb canister, they knew there were enemy combatants in the area and they'd have to pull up fast.
I still like to buy smoke bombs from military surplus stores and entertain my kids with them. They put out a lot more smoke than the kind the fireworks stores sell.