That is an engine notification - when you raise your binoculars, the game notifies you "binocular_enter"; when you lower them, it notifies you "binocular_exit". You don't have to do anything. The game does it for you.
They are left over notifications from COD:United Offensive - in that game, you fired artillery with the binoculars you acquired when you were a certain rank. The game notified itself that the binoculars had been raised, and then there was a function to monitor for the attackbutton pressed. Then, it targeted what the player was looking at, and fired the artillery on their position. It ended on lowering the binoculars with the notification "binocular_exit".