After you maker a Custom Spray.

Does anyone know what file you put it in.

and the name it should be.

never did custom sprays.

ps - mapping q&a

Hmm yes it may seem like a mapping question in some kinds... You'd get more chances in the models/sprites/animations though.
They'd explain you how to get a program called DecalConverter.exe to create tempdecal.wad
(aha, a wad) and place it in the day of defeat folder.

Decalconverter will need a BMP, size divisable by 16 eg. 32x32, 48x96, etc. Your image cannot be bigger than 15.7kb size in bmp format. Pure blue RGB 0 255 0 will appear transparent.
Can be done manually by people who have Wally.

i still use an old program called half-life logo creator