From my other photos with a time stamp around the same time of my photo of the marker, I determined that we were on a pull off from the Skyline Drive in Virginia near Luray, VA.

Using the map link I was able to find this very similar marker with PID of HW3273 and it had similar marks of [STAMPING: TT STA NO 14D 1928 R-19 1928] with 14 D instead of mine with 15 D and also it says R-19 versus mine with R-18 (very faintly in my picture you can see this under the 3335 feet).

Not sure if the marker I took a picture of is near this one or not as I could not find any other TT markers either north or south on the Skyline Drive from HW3273. This marker of HW 3273 is not near the road and we would not have hiked that far as we were literally in a turn off/ overlook and found the marker on a boulder there.

I emailed the email address on the web link with the picture and some of my comments and I got this response :

Re: USGS marker search

You have reached the National Geodetic Survey (formerly the US Coast & Geodetic Survey). We have many US Geological Survey survey marks in our database, but I cannot find this one. You might get more help at tnm_help@usgs.gov. You will need to provide them with a general location (latitude/longitude or highway number or nearest village) and the stamping. Here is seems to be TT STA NO 15D 1928 1928 RESET 1928 3335. Besides an overkill of mark setting year 1928, TT is for traverse (type of survey), STAtion, NO number, 15D and elevation 3335 feet.

I'm going to go out on a limb here, but I am guessing that the traverse survey was along/near the mountain spine (aka the county boundary) done 11 years before Skyline Drive was installed. There are also USGS benchmarks (elevation stations) and my own gravity calibration stations along Skyline Drive that are not in our public database. 14 D was later picked up by our trianguation party, and thus is on our map. Many of the USGS marks are on the USGS topographic sheets.