It's a step in the right direction. It prompts people to think about something worthwhile and could easily become an ice breaker within a community. At the very least it may spark an idea in someone who reads it. "What does it really mean to 'make a difference'?" That can segue into powerful thoughts. Even the simple action of physically presenting a hope or dream can be motivating.

Of course, it's always up to the person to act but I find it's easier to work toward a goal when my spirits are high and being surrounded by hope has an uplifting effect.