hey. i'm trying to make a custom texture for the map im making, but it never shows up in hammer. i will include the vmf and vtf, so if you spot something, please tell me

You've got the basetexture path wrong. It should be

"$basetexture" "maps/hard_paint/sign"

All paths in a material file are relative to the materials folder.

did that, still doesn't like it. it won't work properly for other peoples textures (and yes, i did install them properly) please help

I just changed the $basetexture value and it worked fine for me. Make sure you are putting your material inside "steam/steamapps/common/portal 2/portal2/materials/maps/hard_paint" instead of "portal2/materialsrc/..."