A drinking establishment where one can legally buy and sell handguns.
Seriously, though, here's what it is. I have the gun in question, BTW, or similar.
This is a Uberti Cattleman in an exploded drawing:
Look at the hammer. It's got the firing pin right on it. The hammer falls, and the pin hits the primer. If you drop the gun with the hammer down, the force of the ground on the hammer spur could fire the gun. Yes, there's a 1/4 cock postion on the Colt SAA design that holds the hammer away from the primer, but the force of the hammer spur hitting concrete
could break the sear and hence defeat this rudimentary safety feature.
The Uberti also has a manual safety, engaged by pushing the cylinder pin release and shoving the pin farther into the frame. However, disengaging this safety is slow and difficult under stress, so you wouldn't want to have do it fast when confronted on the trail by a rattlesnake or something.
Now take a look at this:
http://www.okiegunsmithshop.com/rugernewmodbh.jpg
That's a Ruger New Model Blackhawk exploded view, but a bit big to put in the reply.
See how the hammer is flat? The pin is mounted to the frame, and there's a bar connected to the trigger (the transfer bar) that only comes up to meet the hammer when the gun is cocked. If you look at the drawing, you'll see a lot more parts than the Uberti (which is essentially the same as the original Colt 1873 Army).
When the gun with a transfer bar is carried uncocked, you can slam the hammer spur all you want and the gun won't go off, because there's no way the hammer will hit the pin, so nothing will touch the primer.
The upside of the old system is that, done right and with the right springs and machining, it's silky smooth. The downside is that you have a 5-shooter. You can load the 6th at the range, right before firing it, but if you're carrying it as a field gun, you should only have 5 loaded.
The new system involves a good number of additional moving parts, but a 6-shooter is really a 6-shooter.
IMO, get the Uberti. Put some Wolff springs in it. Carry 5. Enjoy it!
That's what I did.