Well I'm not sure about it being a signal but red pills are typically for stimulants.
Absolutely, red has quite a psychological affect, that's probably why stimulant pills are generally red or orange.
I was thinking about purchasing a new vehicle and saw a nice red one I liked. Do you like red? I don't mind red but understand that one of the first colors for prehistoric art was red pigment made with ochre. I remember reading that before, and it was quite a precious dye many years ago. Sounds interesting, did you also read how groups like the Mayans or Ancient Egyptians wore red on their faces during ceremonies? No, but it's amazing how the color can have so many different meanings, depending on the context. Red has many shades as well right? Well I don't know about many but it does range from yellow-tinged scarlet to blush-red crimson and has varying shades as well like pale red pink. Sounds like a lot to me lol! Does the color red signal anything also?
For example, red or orange pills are generally used as stimulants.