[andrewla]

To answer your question directly, at least in New York -- yes, you need to pretend that you're someone on a list, and were that person to later show up (or if they had shown up and you tried to pretend to be them) then there would be an issue. In New York this entails giving your name to the official, and signing your name next to your entry in a big book that lists all registered voters in the precinct, after which you are issued a ballot. New York is not supposed to ask for any identification, unless the voter is missing from the rolls.

I assume it is similar in California. Some research indicates that in California, if this is a new registrant, then some identification, or at least proof of residency, must be provided [1]. If documents cannot be provided to the satisfaction of the officials, then a provisional ballot will be offered instead, pending verification of residency.

[1] http://elections.cdn.sos.ca.gov/regulations/hava_id_regs_fro...