You can use tribe App Store to install the sign-up wall on your community.
Having sign-up wall installed means that while a content is being indexed by Google, visitors still would need to sign-up to be able to see the content fully. The users who are not logged-in can only see the first few lines of a content, not the entire content.
Therefore, when you publish an interesting content on your community, people would not just read it and leave the community. They will need to sign-up into your community to access the entire content.
However, please be advised that the sign-up wall does not make your community completely private. If you want a more private community, and you want any content of your community to be available only for the logged-in users, you need to activate the private mode: How to activate private mode in my Tribe community? 163In this case, users who are not logged-in won't be able to access any content or page of your community.
You can easily install Sign-Up Wall, or other apps available, on your tribe community. Please click on the link below to learn how you can install an app: How to install an app to my tribe community?98