Oops, completely thought I knew what I was talking about, but got it all wrong..
I was thinking of the RM off of the top of my head, maybe I had the FM confused. I apologize for that mistake.
PA 1502 is the one I was thinking of, Wurzbach Pkwy in San Antonio. Its Exit 169 on I-35.
Personal opinion here: I don't even think anyone realizes these exist. I wouldn't put too much, if any, time into this system.
I can tell you, having just been in Corpus Christi, PA 1604 is not signed whatsoever.
Guess I'll begin checking myself before I make posts on a whim