If you haven't heard of Nextdoor, they are the leading social network for neighborhoods, allowing people from the same neighborhood to privately engage &...View More connect on community-specific topics like local events, meetings and even emergencies like a lost pet. The truth is, others have tried to pull off this idea in the past & they failed, but since it's 2012 inception, Nextdoor has been gaining momentum and I think this clever postcard strategy of theirs has a lot to do with it. If you think about it, not everyone in your neighborhood is going to have each others emails and they might not even be friends. This makes a postcard invite a great option, especially when Nextdoor handles everything. It's easy, indirect, & yet contains a personal message & association that acts as a rapport builder. If someone desires to invite their neighborhood (which will create a better user experience for themselves), all they have to do is request to send postcards out to their neighbor's addresses, for free! https://help.nextdoor.com/customer/portal/articles/805411-sending-postcard-invitations The postcard swiped here is an example of what you get when one of your neighbors invites you. It's simple, is personalized & if you type in the invite code, it even pulls up your address for an easier sign-up. Overall, it seems like a fantastic strategy for getting sign-ups & increasing engagement. For great complimentary reading on Nextdoor, check out this article: http://readwrite.com/2013/04/11/nextdoor-hyperlocal-digital-citizen-neighbor