Before carrying or transporting in vehicles on the public highway milk for sale in the town, each dealer shall cause the number of his certificate to be legiby placed and kept in a conspicuous place on each side of the outer side of all carriages, wagons, carts, sleighs or other vehicles used by him in the conveyance and sale of milk,
('66 Code, § 40-5) Penalty, see § 116.99