In California, If you are on probation, you CAN vote. See what the rule is in every US state: http://www.nonprofitvote.org/voting-as-an-ex-offender.html . In California, if you are an ex-felon who is not incarcerated or on parole, you may register and vote.
If you are houseless, you CAN vote.
Someone without a “residential address” simply registers by describing a street corner in the area where they are living (for example, NE corner of J and 8th), then provides a mailing address.
People circulating the Eureka Fair Wage Act can also help you register to vote.
To sign the Eureka Fair Wage Act petition, you have to already be registered to vote, or register at the same time as signing. You also need to live where you are able to vote for the Eureka city politicians and city propositions.