Check this page: Model RR Electronic Circuits
Here is the Dual Alternating Flasher Circuit that will do the flashing lights. It uses power transistors that will flash almost anything, you could also use smaller transistors for a single bulb in the dual signals. I suspect the 2N3055's would probably drive half a dozen signals. 
Here is the IR Train Detector that you can build to detect the presence of a train.
Here's a board from WEHONEST on eBay. IR/Magnetic Presence Detector
I bought some of these, they come with IR and reed switches so you can do block detection using IR or a magnet in your trains. The magnetic option is good if you only want a specific train or two to activate the signal or other device.
