Clause 18

If any person trespasses on any land forming part of an aerodrome licensed in pursuance of an order under section 3, or of a Government aerodrome, he shall be liable on conviction to a fine not exceeding five hundred dollars:Provided that no person shall be liable to any penalty under this section unless it is proved that, at the material time, notices warning trespassers of their liability under this section were posted, so as to be readily seen and read by members of the public, in such positions on or near the boundary of the aerodrome as appear to the court to be proper.