In this era of rampant personal anonymity parishes often say that while they have a guest book few people sign it. To help convince visitors to actually sign your guest book one approach you could consider is to make a modest cash (or in kind) donation to a local food pantry for people who sign. You could mention this in your bulletin and occasionally in announcements and put a little sign next to the book to the effect:
"Please sign our guest book. We'd like to get to know the good people that visit our church AND keep you/them aware of events... AND we'll make a donation to the xyz food pantry."
It still may not convince "Mr. Anonymity" to reveal his identity - but the donation policy projects an image of outreach to the guest and could help emphasize to parishioners that:
- Charity is good
- We want to engage with local charitable entities and
- We value names of interested people because we have something to offer. Invite your friends to church.