This is a component within a railway signaling system that detects the presence or absence of a train on a specific section of track. Manufactured by Siemens and General Electric Railway Signal Company Limited (formed in 1926 by Siemens Brothers and GEC combining their railway signaling activities). This indicator is cased in a solid brass casing with a thick glass cover, and the initials SGE for Siemens & General Electric features prominently at the top of the casing. Dimensions: 10.5cm diameter and 8cm thick.