How does it handle spam?
And a 2-party QR code protocol for adding contacts in person: https://code.briarproject.org/briar/briar-spec/blob/master/p...
In short, both these methods of adding contacts require both parties to actively add each other in the same time period. So even if you post your briar contact code publicly, only the contacts you are adding as well will be able to connect with you.
Briar also has the ability to introduce contacts to each other, so while it doesn't support totally public forums, you can spread information between contacts fairly effectively.