Cool, thanks for the replies, I read about the weight class ID for the changeable bridge plate (the "C" is displayed with a trailer as in "Combination vehicle"), the symbol I didn't see before. It's not an eight, so I am unfamiliar with this type of marking.
Reference:
TM 9-2320-209-10-1, page 1-6, table 1-1
According to this, for my model of truck, it's a 6 unladen, and 8 laden off-highway, and an 11 laden on-highway. Notice this info does not reference a combination vehicle (towing a trailer).
So, the colon is an "8" or is it a colon inside the circle?
By the way, I read a different post stating that the numbers do not directly relate to tons, but rather a calculation based on tons divided by axles. It's just an arcane engineering table set up to make it easy for people to determine whether their vehicle will collapse a bridge or not.