Holmes: The glow at sunset is probably a simple optical effect – the sun's light striking the old glass panes of the station's roof and reflecting off dust or old paint. It could also be the result of a chemical residue from the old gas lamps that still leach into the air, giving the platform a faint amber haze. As for the symbol, it might not be a cryptic clue at all; many abandoned sites have graffiti left by passing travelers. If the symbol is consistently there, though, it could be a marker left by a clandestine group or an old station sign that survived the demolition. Check the paint layers, and look for any documentation about the station’s history. That should give you a starting point.