Section 124 of the city's traffic regulations forbids operating an advertising vehicle, but permits putting of business notices upon business delivery vehicles. The appellant agency is engaged in a nationwide express business. It operates about 1,900 trucks in the city and sells the space on the exterior sides of these trucks for advertising, for the most part, unconnected with its own business. It was convicted. The state court concluded that advertising on vehicles constitutes a distraction to vehicle drivers and pedestrians and therefore affects the safety of the public in the use of the streets. D contends that the regulation violated equal protection because it did not apply to business notices upon business delivery vehicles if the vehicles were engaged in usual business or regular work and not used merely for advertising.