I do think a Journal for our Guild or Aven house is a interesting idea, especially for friends/acquaintances to leave messages for you. An option to set whom can send you a message should be applied to avoid unwanted comments from rude individuals or people who post those false, gold selling sites.
An option to add/update additional text or screenshots can be placed in the Options section, if you do not have interest to keep your Journal in your bag.
In regard to the note idea, I thought the Bulletins in Aven were an option to share messages to other players. I suppose an additional Bulletin could be implemented in to the game to post those notes if not that idea you have shared, so general information can be added and can used as a way to bring awareness and you do not have to trade or sell them.
I do enjoy that idea, especially if there can be an option to display a notice in the World Chat that messages have been added to that Bulletin.
Good suggestions, I hope other players will comment on this also.