Literally just did this today with an 2x2 sheet using 3 channels for 12 decals to a texture(grayscale), worked quite well. I had to combine the link Fwap posted with another one that I can't find right now but it basically got rid of the bleed that was caused...It had a custom node setup with the code - return…
I once built a material to handle a set of decals that worked in multiples of 4 (you could concievably do it with any number but the math gets real tricky), I'd have to rebuild it for a screenshot, but the basic principle is that you essentially just use the tex coord, hook in 2 scalars with an append node to pull in your…