British railway hand lantern manufactured by G. Polkey Ltd of Birmingham. The "SR" marking stands for the Southern Railway, one of the "Big Four" British railway companies formed in 1923. These oil-lit lanterns were used by railway staff, such as guards and signalmen, for signaling train movements. By turning the top of the lamp, different colored lights (white, red, green) could be displayed through various lenses and filters. 
This lantern has a nice brass makers plaque and number, all glass is in excellent condition but unfortunately the clear glass filter is missing but the others are all present.