Unfortunately any such scheme nowadays would be a lucrative target (to say the least) for bots and mechanical Turks. It would basically just become another SEO metric.
Instead you can exclude a specific site using "-site:example.com". This works on at least DDG and Google. Now, if only search engines would let me save those exclusions as preferences (even in a cookie, in case of privacy-focused search engines like DDG) I could blacklist a whole bunch of high-SEO crap sites. That would be a game changer: one black pattern and you're out of my search results.
Instead you can exclude a specific site using "-site:example.com". This works on at least DDG and Google. Now, if only search engines would let me save those exclusions as preferences (even in a cookie, in case of privacy-focused search engines like DDG) I could blacklist a whole bunch of high-SEO crap sites. That would be a game changer: one black pattern and you're out of my search results.