Now I have my map with lots of custom textures and a few custom decals. Now the decals are set up alright ('{' prefix, the last color in the palette isn't white, the decal is in grayscale).
It also shows up on my map in hammer, although when I load the map in HL, the decal's don't show up.
After a few runs, I've noticed that it writes "Can't find decal "<decal name>" in the console. I've checked the wad and it's there!
So how come my custom decals don't show up?