Can my site be indexed without allowing guests access?

Not sure if this is possible, but I thought I would ask. Is it possible to allow Google, Bing, et al, to crawl and index my forums and topics without allowing guests to see posts?

The reason being, unlike most sites we really want to keep prying eyes from reading our discussions. At the same time though, we want potential members to be able to search and find my site and then hopefully register.

Edited to add: Our site isn't porn or anything like that. We're just trying to keep the secret of Santa Claus alive for young children.

Edited October 25, 20159 yr by Michael R