Hi
@EmperorDuncan
I'm so very sorry I missed your message, I haven't been very active here and I hope I'm not too late!
The black crossing signal is lit with incandescent lights. The lights they're installed with are really tiny incandescent light bulbs, less than 3mm I believe and they come with one wire/lead per bulb so I learned. Since there are four lights I think there are four wires each, plus a 5th wire, that being the common so the lights can alternately flash.
I don't think it's possible to add rear-facing flashers to that kind of signal, especially with bulbs. You can try but I don't think you can. But if you want to make the signal bi-directional, your best bet would probably have to be to remove the original lights and light housings and the cross-arm that connects the two lights and replace them with a completely different set of lights and light them with LEDs, which are way more efficient. That might be too many incandescent bulbs to put on one signal and on a flasher unit, especially if you try to light or flash more than 8 bulbs at once and you could fry your flasher unit (speaking from experience!)
I've had Model Power signals too and they're different from the NJI lights. I forget if the MPD signals are bulb or LED, I didn't have them for very long and they stopped working on me, much to my sadness! But I don't think you can or should use them to back-mount your NJI cantilever! As I said the MP signals and the NJI signals have different kinds of lights and brackets and the lights have to all be the same. Otherwise I wouldn't do that if I were you!
I have two of the black NJI cantilevers but I had to replace all four lights on one of them. I used grain of wheat light bulbs to replace the original bulbs, I think it was one of these
or the ones from Model Power
Both available on Hobby Linc
https://www.hobbylinc.com/faller-12-16v-grain-of-wheat-bulb-red-model-railroad-light-bulb-180672 But it was a drag installing the new bulbs into the signal and wiring too, especially the upper signals, being how wide the wires are, and you have to string one wire at a time through the holes and make sure they all come out of the base of the signal! But it's doable to replace the bulbs!
I don't know how to remove the STOP ON RED SIGNAL sign, I never tried to. Personally I like the STOP ON RED SIGNAL sign on the signal. My best guess is to use a razor sharp knife or razor blade and slowly saw it off.
I'd ask other hobbyist or model railroaders about all that because my advice might not be legit and I hate to be the reason your signal gets more messed up than it is!
I'm sorry if I wasn't much if any help, but I hope you can try something!
Have fun! (My way of saying "good luck" since I don't believe in luck but want to show I do care.)
If anyone else reading this can help, please oh please do so!