Jim is right on target when it comes to single action revolver designs that have come down to us from the 19th century, or were made during that time period. Any antique, or copy thereof that doesn't have a transfer bar safety should be carried with the hammer down on an empty chamber. Period!
Some of the Italian single action reproductions have a safety built into the hammer. They did this, because without something their products couldn't be imported into this country. Others depended on a long basepin that could be pushed back and locked by the basepin latch after which the back of the pin would block the hammer. The problem with this was that very few that had it really used it. Too much trouble to put it on and take it off. In my view such safeties are worse then none, and the proper solution is hammer down on an empty chamber.
Any revolver (or pistol) can be completely safe when carried with an empty chamber in front of the firing pin, but this is less then desireable if the handgun is being used as a weapon.
All of the mainline hand ejector revolvers (where the cylinder swings out to the left to load) made after World War Two are safe to carry fully loaded. In particular, all Ruger double-action revolvers are safe to carry fully loaded, but pre-1973 single actions are not unless they have been modified with the kit Jim mentioned. Many pre-war double-action revolvers are safe to carry fully loaded, especially Colt's. But others should be evaluated on a case-by-case basis. The same can be said about any automatic pistols.
In the end it is the owners responsibility to know and understand how the safety(s) on their handguns work (or don't as the case may be) and carry them accordingly.
