Tim (TKB) we have two different subjects going on here.
First would be marking required for electricians.
As you found only if you decide to letter your truck do you need to include the license number.
Than there is DOT truck lettering which kicks in over a certain weight class. Vans are not in that weight class. If I remember it is for commercial vehicles over 10,000 gross.
This would be the lettering that includes the gross weight rating of the truck and the owner/operator info, as you see on big rigs.
