It all depends on color as to what it would mean there were a lot of different color lanterns and each represent a certain condition that the train crews or other departments have to comply with.
We still use some of these today but with radio communication being reliable most of the old lanterns and lamps have no use we really only use red which means stop, blue which means there are mechanical forces on the equipment and it cannot be moved or coupled into without mechanical giving authority, there's also a white light that goes on a track where there are occupied cars such as coaches or track dept employee office cars.
