Lookout
A lookout or look-out is a person in charge of the observation of hazards. The term originally comes from a naval background, where lookouts would watch for other ships, land, and various dangers. The term has now passed into wider parlance.
Naval application
Lookouts have been traditionally placed in high on masts, in crow's nests and tops.The International Regulations for Preventing Collisions at Sea says in part:
Lookouts report anything they see and or hear. When reporting contacts, lookouts give information such as, bearing of the object, which way the object is headed, target angles and position angles and what the contact is. Lookouts should be thoroughly familiar with the various types of distress signals they may encounter at sea.