By playing around with the URL, you can actually discover the names of all the existing campaigns on Roll20. For example, if you visit this page: <a href="https://app.roll20.net/campaigns/details/18888745/" rel="nofollow">https://app.roll20.net/campaigns/details/18888745/</a> , it redirects to <a href="https://app.roll20.net/campaigns/details/18888745/fallen-realms" rel="nofollow">https://app.roll20.net/campaigns/details/18888745/fallen-realms</a> . You can’t access the campaign itself, but thanks to the redirect, you now know the name of one of my campaigns.
The first thing that came to mind was to check out the earliest campaigns created by the developers. I’m not sure if I should actually recommend hiding this kind of information, since it’s not really a security issue. Still, I thought I’d share it because I found it oddly fun to mess around with. A possible workaround is to avoid this redirect and don't disclose the campaign names at all.