In my opinion the only way to tell if a 38 Safety Hammerless with a 2" barrel is by a letter of authenticity. There are no clear ways the factory marked these guns. It is very rare that you find one with the patent roll marks on it. I have a 2 short barrels (less than 3 1/4") that have factory roll marks on them. One is a lettered 2 1/2" barreled gun with incomplete patents on the top. The patents start just before the front sight and run to the back of the gun. The patents are incomplete because they are longer than the barrel rib. I have another unfinished (in the white) 2 1/4" 38 Safety Hammerless barrel that has the same incomplete roll marks that start just behind the front sight and are rolled towards the back of the gun.
Cut barrels will most often have the the front part of the patent roll marks under the front sight showing clear evidence the barrel has been cut.
If there are no patents on the top rib, its a gamble if its a factory 2" barrel without having the letter. At that point I look at the serial number of the gun, the end of the barrel, and the front sight pin. Most factory 2" 38 Safety Hammerless guns are serial number 258,000 and higher. Its my opinion that serial numbers before 258,000 with a 2" barrel would be a special order. On a factory gun the top rib is recessed and the end of the barrel is radiused. The front sight should be the standard height and have an unmolested front sight pin. After that I look at the finish, and the condition of the grips compared to the finish.
To me, if those conditions are correct, it very well may be a factory 2" 38 Safety Hammerless gun.
I looked at the pictures of the auction for this gun. There does not appear to be a factory letter. The good is that it has a serial number in the 260k range, the end of the barrel looks like a standard factory treatment, and there are no roll marks on the top rib of the barrel. The bad is the front sight has been messed with and is shorter than normal and the wear on the grips looks to be more worn than the finish on the gun. In my opinion this gun has a 50/50 chance of being factory original.
For these reasons most collectors don't buy a 2" 38 safety hammerless gun without a factory letter.
I have one with a 2" barrel that wears serial number 260,38x. I don't have a letter for it. It has a pinned front sight that looks factory, the end of the barrel looks correct, and it does not have any patent roll marks on the top barrel. The finish on the gun is consistent with the wear on the grips. It has the caliber stamped on the right side and the words SMITH & WESSON stamped on the left side. To me the gun looks like its factory original so I took the gamble and bought it.
I just added pics of the gun listed above. The front sight is taller than it looks, the angle of the camera makes it look shorter.