@mark is a tool for you guys to add a description to the environment. Examples are a description of a sight of slaughter, a blood trail, or a note written in sand. You should not use @mark for things where you have other means to get there like the mentioned posters or letters. You should also not use @mark to make statements that would need DM approval. However we DMs sometimes also use @mark to do just such. So in case you stumble upon such a note and are wondering - simply ask on the DM channel. Also don't use @mark to describe certain emotions / mental states evoked in the PC stumbling on it and don't call for lore / spot / listen etc. checks.