You will need to be a bit clearer in your request though in truth few commercial signals are available. i believe that a few manufacturers have made searchlight signals though you did not state your scale.
First off, are you looking for just a model of signal? and then a semaphore or a searchlight? Finally a single head or double headed signal.
Or are you looking also for the logic that goes with it to drive the signal aspect? This is far more difficult for two reasons. First the electronics must be weatherproof for use outside and more importantly, signal logic is very complex. The real railroads used several different types of signal logic (all the way from ABS to CTC) and these all required different logic sets.
As you can see, building a model of a signal system can be a fairly complex undertaking depending on how close to accurate you wish to be.
The current issue of the Modellers Annual has an article on a building a very nice F scale (1:20.3 scale) semaphore.
Or are you looking also for the logic that goes with it to drive the signal aspect? This is far more difficult for two reasons. First the electronics must be weatherproof for use outside and more importantly, signal logic is very complex.
Not really. This is an extremely simple system that I came up with that uses nothing more than relays, a wall wart power supply, and rail insulators. The system uses 4pdt relays. Three poles are used to make the system work. The 4th pole is free to run your lights, semifores, etc.
A little more complex, this is the system I devised to control trains at my "X-ing" where I used to get "corn field meets." I've documented these systems on this site in the past and you should be able to do a search for the Tortoise Bump Accident Sentinental System (Bump A.S.S.) to get the full story.
You did not say what type of prototype signal system the logic you showed was supposed to emulate making it impossible to judge whether the relays really do the job or not.
Regards ... Doug
I don't understand the comment nor see the need for prototype logic???
For the first diagram, when a train engine or any railcar with metal wheels crosses a gap, that relay activates turning on that block signal/semifore/whatever and turning off the one ahead and one behind. It stays on until the train reaches the next relay. Can't get much simpler than that.
The second system turns on the signal when the train/railcar crosses the gap for whatever time is set on the 555 chip, then it goes off by itself. I use this same circuit to turn off the block for an opposing train at my crossing when the first train to arrives and occupies the crossing.
I appreciate that your requirement for a signal system is different from the prototype and that you simplified the logic to fit. That is why I asked the question in the beginning pointing out that to accurately model a real prototype signal system is not as easy as many folks would think ... and if an accurate model is what is desired (it is certainly what I would desire) then some real effort is needed.
Just as with cars and locomotives, if an inaccurate and simpolified model will do, then by all means go to it. After all, it is your railroad ... I only asked that the question of how good is good enough be clarified.