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Explanation: If you're talking about signals, this might help...
Fixed (Wayside/Lineside) Signals by Style (hardware)
Old / Obsolete Fixed Signals
List of active semaphore signals in U.S. [off site, Eric Schmelz]
Color Light Signals: US
Position Light Signals
Color Position Light Signals
Rare / Unusual Installations
PRR Tombstone Signals: -1- -2-
Significance of Signal Components (N. America)