Any person engaging in or prosecuting any business, activity, trade or employment contrary to this article, whether without obtaining a license therefor before commencing the same or by continuing the same after the termination of the effective period of any such license, shall, in addition to paying the license tax, be liable to the following penalties: If the license tax to which he is subject is an annual one or for a period of one month or more, 25% of such tax for each month or part thereof during which he had been in default; or if such license tax is for any period less than one month, ten percent of such tax for each such tax period or part thereof during which he has been in default. It shall be the duty of the City, by its duly appointed agent, to collect the full amount of the license and penalty therefor.