The designers of some military rifles saw fit to not fit a safety to their rifles, though the MAS-36 and the later version are the only ones I know of. They have rather heavy trigger pulls. The Mosin-Nagant has a safety, sort of, but is extremely awkward to use. The Swiss K-31 has a safety that works exactly the same way but there is a convenient ring that makes it easier to use. I never found the Mauser type safety, also used on the '03 Springfield that easy to use, at least when it was stiff on any particular rifle.
Then there are pistols and revolvers. Until recently, revolvers have mostly been free of positive safety devices, though I am not referring to the rebounding hammer feature found on most, but not all, revolvers, and actually called the positive safety on Colts. However, some surplus revolvers were retrofitted with a safety to block the hammer or something. Or so I understand. I've never examined one so modified.
The problem is the intent of these latter day safeties, which is more of a security feature than a safety feature, if you follow me. I wonder how the folks at Glock are looking at this, assuming they are. After all, Glocks do not have any active safety feature, in a manner of speaking. They may be drop proof but nothing is present to prevent the gun from firing when the trigger is pulled, assuming there is a round chambered. Since one of the steps in disassembly is to pull the trigger, well, you can see why there might be a few accidental discharges now and then.
Grip safeties were common for some reason when automatics first became popular in the first ten or fifteen years of the last century. Even Lugers had them. Now I think only Colt 1911s and copies have them. For a while it was popular in certain circles to pin down the grip safety so you could shoot with a "thumb up" grip.
I don't think the Shanghai Police did that but they did pin the safety down on their issue Colts, both .45's and .380's. They, meaning mostly Fairbairn and company, I guess, went out of their way to make sure no mechanical safety would get in the way. Needless to say, cocked and locked was out of the question.
I have never been that comfortable with safeties, at least on rifles, especially the little sliding safety you find on shotguns and on the Ruger No 1 and 3. It just doesn't seem like there is enough there to work, as if I could just pull the trigger and break a piece of steel. Perhaps another way to look at the problem is that safeties don't always work because they aren't always applied, just like seat belts.
Did you know some horse drawn wagons have seat belts?