I was looking at the Post on affordable railroad signals. Wow Less than $4.00 bucks for a signal is cheap. I probably couldn't build one that cheap. but, I have scratch built my own signals.
Base Mast Signal Head
The Base 3/4 Conduit + Sheet Styrene
Add Plastruct Ladder Platform - and Brass Wire for handrail
Install on Layout This signal is a different one from the one I show above. The Searchlight built in the same way. This signal is an exit signal from my yard lead. Signal change from green to red, using an Atlas Twin ( DPDT ) on my control panel. The searchlight is connected to a relay wired to an outside control rail.
Semaphore ( NJ International ) controls the other end of the yard Lead. It is controlled by a Tortoise Switch wired to the same Atlas Twin. Note my other signals behind the Switch Tower.