It's probably best if I quote my e-mail to Rich, sent right after I found this mark:
"The weirdest thing just happened. I was working on my site for too long, and needed to get out for a little walk around the block. Well, you won't believe this, but on the little bridge over Sterry Creek just down the road (across from the In & Out Mart), there is a benchmark! It's sitting right on top of the side wall of the bridge. I don't see how I could possibly have missed it before, it's that obvious — and I pass that bridge at least twice a day (and probably at least once a week on foot). In fact, I was standing there just a few weeks ago when my father and I went for dinner, showing him the creek, and didn't notice it. I could understand it if it looked like a newly-set mark, but it looks like it has been there a long time! It's a PennDOT mark (the newer kind, not the old PDH style)."