I buy the heavier duty ones (auto part store ~ Napa, Car-Quest, etc. . .) and tighten them down not with a screw-driver but rather with a ratchet set and tighten them tight enough that it would be very difficult if not impossible for someone to remove them with a screw-driver but would also need to use a ratchet set. So far no theft issues with that but then I don't live in the city and where I live vandalism and "funny guy pranks" are more of a problem then theft. When I walk back out to my bike after being in the store for half an hour I'm not looking to see if anything is missing I'm checking to be sure someone didn't let the air out of the tires smeared dog poop on the seat or put grease on the brake pads or disks or opened the quick release on the seat just enough for it to hold until I sat on it and then it will slide down or the worst one of all, reached down and bent the end of my derailer in far enough that when I shift into low gear it will grab on a wheel spoke and tear itself and or the wheel apart.

If they do anything to my lights it probably won't be to steal them but to hit the lenses with a shot of black spray paint or some &@#$^! like that.

If you are worried about the hose clamps leaving a mark on the handle-bar tube then wrap some tape around the bar before tightening the clamp down onto it. I don't care but if you do on either the bar or the flashlight or both tape wrap under the clamp.