On: Ask HN: Better to have optional signups or force signups/logins?

browsers are surprisingly unique to each user; see "browser fingerprinting" https://panopticlick.eff.org/

You could also just use cookies, which is perhaps a more socially conscious way of handing it.

Browser fingerprinting fails for cases where a computer is shared. That includes both home and public terminals. Not to mention it creeps people out and lacks any type of security.