All moneys received from such levy shall be paid into a special fund to be known as the “band fund”, and no moneys shall be appropriated out of such fund until the mayor and council, board of aldermen or board of trustees shall have first entered into a written contract with the authorized officials of a band for its employment in the giving of free band concerts, or equivalent musical service by the band upon such occasions of public importance as shall be stipulated in said contract. Any band entering into a contract under this law shall be known as the municipal band, and shall administer its own financial and business affairs. No voluntary contribution, donation, or diversion into another fund shall be made from this fund in any manner whatsoever.