A privately owned yellow van pulls up ahead with "SCHOOL BUS" lettered on the back and a stop arm fitted to its side. Could that be a vehicle dressing itself up as a school bus?

Correct answer: B. No — only a school bus may display those words or be fitted with a stop arm, and chrome yellow is reserved as well

Not lawfully, and that is the point of the rule. The Highway Traffic Act defines a school bus as a bus that "is painted chrome yellow", "displays on the front and rear thereof the words 'school bus'", and displays on the rear "do not pass when signals flashing" or "do not pass when red lights flashing". Section 175(4) then shuts the door on imitators: no motor vehicle other than a school bus may have those words displayed on it, or "be equipped with a school bus stop arm", and s.175(5) makes it an offence to drive a vehicle that breaks the rule. The chrome yellow colour itself is reserved too — s.175(3) allows it only on a bus used to transport children or adults with developmental disabilities. So the markings are a reliable signal, which is exactly why the law protects them: you are meant to be able to react to the colour and the words without first working out what the vehicle is.

Source: MTO Driver's Handbook: Highway Traffic Act, R.S.O. 1990, c. H.8, Section 175(1), (3), (4) and (5) — definition of school bus, chrome yellow restriction, and school bus signs