The guy I know who got pulled over was asked to prove his tow rating. He had the owners manual and original window sticker which showed the axle and spring package. The owners manual told the rest of the story. I am guessing they can get the info real quick. If not they will ask you to follow them to a DOT approved weight station until you can provide the necessary info. A boat dealer I know got busted in Georgia and was held up for 36 hours until a suitable truck was obtained. He was towing with a 2500 Dmax and they had to get a 3500 Dodge Dually due to being overweight while bring back a boat from Naples FL to Indiana.
I have a Towing Guide Manual that I bought from a major marine publications that goes back to 1998 and list all the axle codes and spring codes for all vehicles plus max tow rating for each. Its simple to use, like looking up a oil filter at Auto Zone. For example: You go Dodge, 2003, 1500, 4x4, regular cab, long bed, auto tranny, 3.73 gears=XXXX# max trailer weight.
I have seen guys along the Highway 67, which I live less than 1.5 miles from and I 69 which I live less than 2.5 miles from, pulled over and being forced to offload stuff onto roll back wreckers. Just last week I saw a guy hauling a load of Jet Skis on a GN and they were off loading 6 of the 30 or so that were stacked on it still in the crates to a wrecker.
Chris