Politicians often use long lists of endorsements on their literature and advertisements, because they think endorsements work, and that's probably true. Yard signs are out there endorsing the candidate 24 hours a day, perhaps for weeks.

Another factor may be even more important in the long run. I remember driving around town looking for Kerry signs so I could offer a Bryan Kennedy sign as well. (It turned out to be a pretty good technique, by the way.) One woman said that was the first time she'd taken the step of putting out a sign and she wasn't ready to jump to two signs yet. I respected her honesty and understood her feelings about going public with her politics, which isn't easy at first. It takes time to get comfortable with that. Having a sign is a way to take that first step beyond just voting in secret, and may lead to more involvement. It also may be the only way that some people (elderly, disabled, too busy supporting the family) can help a campaign, and it's good to give them that outlet.