In the theater business we all say (scream) “HEADS” when something bad is about to come from above. We do a lot of work up high and it’s pretty much the industry standard warning.
Oh, and saying “ohsh*tlookoutheyyoududedudedude… (thwack) sorry”
ROCK! In rock climbing…
Um, try HEADS! CLEAR! COVER!
RUN LIKE HELL, YOU’RE GONNA GET CLOBBERED!
Though that last might take a little too long. Mostly try to warn people to avoid working under you. And for heaven’s sake, they should be wearing helmets.
I have always been told that when someone yells “FORE” on a golf course, the absolute worst thing you can do (which, of course, is exactly what most folks actually do) is look for the incoming golf ball. You’re just exposing your face to the hazard. What you’re supposed to do (and what the folks I play golf with all do) is to turn in the opposite direction, duck, put your hands over your head, and count to ten. Broken hands and bruised backs heal a lot better than broken skulls.
I think more injuries should occur on the golf course. That would make watching golf on TV possibly bearable. It should also be set up like a race where even getting to the holes in a timely fashion helps your overall score. The golf carts could be designed like minature race cars and the players can wear numbered jerseys with lots of padding because they may get run over!
When does football season start again?
I guess you couldn’t just rope off the area under where you’re working? Or at least tell people to stay the hell out from under you, because you will be dropping stuff. Drop a ballpeen hammer early on so they know you’re not kidding 
. Then say “whoops”.
I could drop random material for effect. But that may damage the equipment these people are actually working on. It`s a testing and R+D facility, so there are lots of sensitive things to break. Even a hard hat may not protect from a 40 lb object at 30 feet and falling fast.
He, He, - I should hang a warning sign on the lift with the definition of “heads” and “clear”.
You could write it on the bottom of things 
To give a serious answer, if you are working with a forty pound anything 30 feet up, then no one should be working underneath you. It’s one thing to drop a bolt or a pair of pliers on someone who is wearing a safety hat, but it’s another thing to drop forty pounds. That could kill someone from that height. I hope you have a safety policy that avoids this sort of event.
(Sorry to be a spoilsport, I’ve seen people killed at work and it’s not that funny)
<Slight Hijack> A golf ball is a dangerous thing! A buddy of mine in High School worked at the public golf course near the school in the summer. They were all required to wear hard hats while working. One day he was raking a sand trap and took off his helmet to wipe his brow… <BAM>
According to the guy he was working with it sounded like a shotgun went off when the ball his his head. His skull was cracked and he was rushed to hostpital! He ended up with minor brain damage…</Slight Hijack>
whuckfistle, if I am ever working under you when you drop a 40lb object, I would ask that you simply yell “RUN!” That may not work with everyone, but in the off chance that it is me down there, I will have no hesitation before I dart off like Bruny Surin! I just want to have a system!
No good cause that’s where you write the disclaimer
:BY ACCEPTING DELIVERY OF THIS OBJECT I HEREBY WAIVE ALL RIGHTS TO LAWSUITS AND REPERCUSSIONS AGAINST THE DROPPER:
LOOK OUT BELOW!
BOMBS AWAY!
Fetchez la vache! [mooooooo…]
I wait until they get hit, and when they look up, I look up too, and go “What the hell just happened? Something just fell past me!”
Works, too.
I guess “Fire in the Hole” only works with explosives…
I generally use “INCOMING!” or “LOOK OUT!” At work we warn each other with “on your left” or “on your right” if we’re carrying something hot and don’t want to get bumped into, but with people who’re not used to that convention they might misinterpret. Or maybe stop to remember which is right and which is left (like me ).