It’s pretty much the same on every cylinder.
Howdy
First of all, your revolver only has one cylinder, the big cylindrical shaped part that spins around.
The holes in the engine block of your car are called cylinders.
The holes in the cylinder of a revolver that you place cartridges in are called chambers, or in the case of Smith and Wesson, they are called charge holes, not cylinders.
Very common mistake with new revolver owners.
OK, now that we have that out of the way, I have many Smith and Wesson revolvers.
This is my Model 19-3 that I bought brand-spanky new in 1975.
I must admit I have never seen marks quite like that on a revolver.
This is the cylinder from my Model 19-3. Ignore the bright area the arrow on the left is pointing to, that is just a reflection. The arrow on the right is pointing to the carbon rings that always appear on the face of a revolver cylinder once it has been fired. Hot expanding gasses escape from the barrel/cylinder gap every time a revolver is fired. This leaves a deposit of carbon and vaporized lead on the face of the cylinder in the shape of a ring, that matches the shape of the forcing cone (the rear portion of the barrel). Lots of shooters scrub the carbon rings off their revolvers every time they shoot them, I gave up trying to do that a long time ago because the rings always return. I always say if you are trying to scrub off the carbon rings, you don't have enough revolvers yet. Once you have enough revolvers, you will stop trying to scrub off the rings. Anyway, what you are seeing on this cylinder is a combination of carbon rings, and wear to the blue on the surface of the cylinder from firing it for over 40 years. Notice too some soot on the gas ring the third arrow is pointing to. If you look very carefully you will see a small amount of soot on the surface of the cylinder flute visible in this photo. All of this is completely normal for someone who does not try to get their revolvers spotless after being fired. (that would be me.) Notice too that your cylinder seems to have a bit more of a bevel running around the front edge of the cylinder than mine does. Not a problem, the amount of bevel sometimes varied over the years.
This is the forcing cone on my Model 19-3. Notice there is a bit of a flat at the bottom of the forcing cone. This is a clearance cut to provide clearance for the gas ring on the front of the cylinder when the cylinder is closed. Without that cut, the gas ring would interfere with the bottom of the forcing cone. Smith and Wesson began cutting that clearance cut in their K frame revolvers (your Model 19 is built on the K frame) back around 1905 if memory serves. It was never a problem with 38 Special revolvers. When when 357 Magnum revolvers began being built on the K frame with the early 357 Combat Magnums (predecessor to the Model 19) in 1955 the thin cross section of the forcing cone caused by the clearance cut started to become a problem. Sometimes high velocity 357 Magnum ammunition would cause the forcing cone to split at the thin spot.
Question for you: Does your forcing cone have a flat at the bottom, or is it completely round all the way around? I understand the newest K frame 357 Magnum revolvers S&W is making have been re-engineered to eliminate the flat spot, but I have not been able to examine any of the new ones yet.
Anyway, I suspect what you are seeing is a bit of lead splatter on the bevel on your cylinder.
Try this: using a piece of soft copper, see if you can scrape the lead off that spot. Use an old copper penny, see if you can find an old Grain of Wheat penny for this. Or else try picking at it with some other type of soft copper. DO NOT USE STEEL OR STEEL WOOL, YOU WILL DAMAGE THE BLUE. Do not use a lead removing cloth either, you will probably damage the blue if you do.
Let us know what you find.
This is a model 19 classic - about 100-150 soft 38 special rounds through it. I understand guns wear in and I dont expect them to look like they did the first day I bought them unless they stay in the safe. 
