$ssbump is a boolean material command that flags the material's $bumpmap as being self-shadowing.
Example
rockwall_cave_02a_height-ssbump.vtf
LightmappedGeneric
{
$basetexture nature/rockwall_cave02a
$surfaceprop concrete
$bumpmap Nature/rockwall_cave_02a_height-ssbump
$ssbump 1
}
Creating self-shadowing bump maps
...anyone know?