The regulation which prohibits any person from allowing his vehicle to stop in a public street for a longer time than twenty minutes, is a valid police regulation. Pub. Sts. e. 28, § 25. Commonwealth v. Brooks, 109 Mass. 355. The fact that the defendant had a license from the State as a hawker and pedler is immaterial. His license does not authorize him to violate the ordinances or police regulations of the city. He is subject to the regulation in question, in the same manner as is any person exercising a trade which does not require a license. Exceptions overruled.