Guild members can leave a message with optional timezone aware time of day or datetime on the board. There is a limit of one or two per member. They can use this to organise events or parties or post guild wish or todo lists. Notes of ppl who leave the guild stay behind for some time, but get a symbol. Nobody but the creator can delete them. This ensures wrongful member removal doesn't undo someones work right away and other members can copy it for them, if desired.
If the hall is public non-members can also rrad them, so maybe they can ask to join an event, even though they're from another guild.

Examples:

"22:00 Daily Shadow Lair. Meet in chess room. Instance with lowest number."

"14:20 6 Aug 2026 Birthday Give Away in war room. Instance with lowest number."

"Please focus on farming for Snarbo trophy first."

"I want training hall! Pls install room."