In my case (Austria, EU), when the police is required to check your identity, and if you aren't carrying some allowed form of identification (id card [most people don't have one around here, no one needs it but it costs as much as renewing your passport], passport [who carries their passport around, might even be expired], drivers license [you might not have one]) they have to follow you home or wherever an recognized identity document of yours may be (e.g. some people store them at a safe deposit box at a bank).
Which is the same thing with cookies, you just set some string in a HTTP header, if the browser actually honors that is up to user (in the way what browser he installs and how the user configures it).
In my case (Austria, EU), when the police is required to check your identity, and if you aren't carrying some allowed form of identification (id card [most people don't have one around here, no one needs it but it costs as much as renewing your passport], passport [who carries their passport around, might even be expired], drivers license [you might not have one]) they have to follow you home or wherever an recognized identity document of yours may be (e.g. some people store them at a safe deposit box at a bank).