This signal displays signal aspects for two tracks. It would usually be placed to the right of all tracks. It's a somewhat unusual signal, with only a single mast on the left side. That head can only display three signal aspects, Clear (green), Approach (yellow), and Stop (red).
The other mast with two signal heads, can display many more signal aspects, such as Limited Clear, Medium Clear, Advance Approach, Approach Medium, Restricting, etc., in addition to the Clear, Approach and Stop aspects.
For a basic "Primer" on railroad signals, CLICK HERE.
