In California, all building contractors and sub-contractors have that same requirement (but different size type). It has nothing to do with getting a business license, but maintaining a contractors license. Been around for years.
From the California contractors board website.
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Plumbing, electrical
sign, and well-drilling contractors must display the following information on both sides of every business vehicle in letters at least 1 1/2 inches high (B&P section 7029.5):
' Business name;
' Permanent business address; and
' Contractor's license number.
All other licensed contractors must display their business names and contractor's license numbers on every one of their commercially registered vehicles. The name and number must be in a clearly visible location in letters at least 3/4 inch high and wide (B&P section 7029.6).
Contractors engaged in interstate contracting can ask the CSLB Registrar for an exemption from the requirement to put their California contractor's license number on trucks and vehicles.
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I don't make vinyl graphics anymore, but have done my share of layouts for contractors and have reminded a few designers doing work in California to make sure they are up to code. Is it a pain, yeah...