Putzing around Prince William County today, I found something quite strange. SR 619, at least between I-95/Exit 150 and SR 646 near Independent Hill, has mileposts along the side of the road. The mileposts count down as you head northwest away from I-95 and are high enough to suggest that "Mile 0" is where SR 619 begins at US 29 in Gainesville.
This is the only time I've ever seen mileposts on a secondary route in Virginia. Heck, most of their primary and U.S. routes don't even have mileposts.
Unfortunately, it was drizzling/light rain out so I don't think I got a good photo. But I'll definately have to head back.