I've found that talking to people asking you to sign petitions (especially ones about taxation and legalizing marijuana) is a good way to spread the message of voluntaryism. We see a lot of them in California during this election time. Presenting the question of "can you delegate a right you don't have" is a great conversation starter...although some may want to chat, some may want to ignore you in attempts to get more signatures. Either way it has worked for me a few times, especially with younger people.