No person shall engage in the business of operating a taxicab or permit the same to be operated until and unless the approved applicant for a license deposits with the Director of Finance and Public Record a policy or certificate of liability insurance for each unit for which a license is applied for, acceptable to and approved by the Director of Law, indemnifying the applicant in the sum of $500,000 for injury to one person, $1,000,000 for injury to more than one person and $300,000 for property damage in any one accident, for the operation of each taxicab for which the license is applied. The policy shall contain a clause obligating the surety company or insurance company to give a ten days' written notice to the Mayor before the lapse, expiration or termination of the policy, and if the same is allowed to lapse, the license to operate shall immediately expire.