You couldn't search with the forum software's built in search feature unless signed in sure, but they were usually indexed and searchable via google, and indeed

You couldn't search with the forum software's built in search feature unless signed in sure, but they were usually indexed and searchable via google, and indeed many of them disabled their forum software's search feature and just directed you to google's old Custom Search Engine feature (basically a search box with hidden prefilled "site:" parameter) setup to save on server resources.