Any permit or variance granted may, if such action is deemed advisable to effectuate the purpose of this chapter and be reasonable in the circumstances, be conditioned as to require the owner of the structure or tree in question to permit the city, at its own expense, to install, operate, and maintain thereon such markers and lights as may be necessary to indicate to flyers the presence of an airport hazard. (Ord. 1022 § 7 (e), 1974).