My office still gets spam faxes to this day. The paper and toner only add up to a few cents a month, so it's not worth doing anything about.
I knew a realtor that had a sheet of black paper with a few choice expletives written on it that they would send back to spammers. There was an art to taping it into a loop so it would continuously feed. This was a few decades ago when a the spam faxes could cost more than a stamp.