In Maryland, the letter of the law says you're supposed to since the signage simply states "if over X,XXX GVWR, stop". (Which, there are 2 very near me that are 10,000 GVWR- which means in my dually alone, I should stop.) That said, I got a wink and a nod in email from a guy from the state highway administration that implied they wouldn't stop a RVer and that I should drive on by.
So Maryland- you're supposed to, but no one bats an eye if you don't.
In Virginia, I pulled in (because I wanted the rest area behind it) and I was directed to bypass the scales.