My Father's Smith & Wesson 357 mag Combat Model 19, for example, does not have the safety mentioned. It was made in the 60s and re-worked for competition to boot
You should not be able to push the hammer forward on that gun, if you can then it's missing the safety component I mentioned before. It's possible to disassemble the gun and leave it out when you reassemble it, so it may have gotten lost over time, but virtually every S&W in the past 70 years has had the hammer block in place.
I happen to know the model 19 fairly well and know for certain that it came from the factory with the block in place. If you are able to push the hammer forward, it's malfunctioning. That is not normal behavior.
Since I've said before you shouldn't believe me, here is a diagram:
Part # 5084, on the lower right.
The only reason I'm so emphatic on this is because if you can push the hammer forward on a revolver, the gun is unsafe and should be taken to be repaired. This presents a substantial safety hazard and most revolvers made in recent times have functionality to prevent this from happening. I've handled one that someone removed the safety from and the amount of pressure it took to move the hammer forward was not that significant, I could easily see how someone could push it forward and activate the round in the chamber. These guns were specifically designed not to do this and starting many years ago (I don't know the date exactly, but pre-WWII), S&W incorporated the hammer block to prevent misfires.
Anyway, take it for what it's worth. I personally wouldn't handle the gun, loaded or not, and what you mentioned is one of the several things I look for when buying a revolver.