[RussEfarmer]

Code:

hook.Add( "PlayerSpray", "DisablePlayerSpray", function( ply )
    return not ply:IsAdmin()
end )

This works fine in my server but IsUserGroup would work better because IsAdmin only checks for admin (co-owner, "adm" is actual admins) and superadmin (owner).. alternatively just saying "return true" would block it for everyone

Other alternatively, doing absolutely nothing would be a good option because people seeing a spray on the server once every two weeks by coincidence has never really been a problem