That's when LEO pulls them over when they pass a weigh station because they know how much an excavator weighs. What's going happen when LEO looks at the registration to see what the trailer's VWR is and sees it's carrying way over it's rating with the portable scales?
Cops don't carry portable scales for nothing. And from what' I've been told, the only reason to get something stickered for a lower rating is to keep the insurance and registration fees down... Because if you get busted carrying more than the rating, you'll be left with a fine, and on the side of the road, or worse towed.
BTW, some States allow vehicles to be rerated, for a fee, at a higher weight rating. People do this .... yes it costs them more in insurance and registration, but they can go through the weigh stations without worry they'll be stopped for being over weight.