A bulletin board stands for news and notices shared with a group. What is pinned there is read as information you are meant to notice, or an announcement you are waiting for.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.