It would be nice to have some way to leave a marker in the nearby terrain of your char, as a way to tell your coplayers "Build ovens here", "Replant stuff here" "Attack on this front section" etc.
Some suggestions for mechanics below, I do not know if they are all sound.
1) You can place a small flag or marker anywhere in the landscape (in your field of vision) by clicking a button (or hotkey) e.g. [a]dventure - [p]ointer flag - leftclick a tile
2) The flag has no collision box and cannot be interacted with except for a hovering name on mouseover - that is if the character looking at the flag has the placing char kinned or memorized.
3) For spectators, the flag will be coloured in the placing chars party colour if they are in a party, as the colour red if they are in village, but not partyed, and in greytones if they are neither partied nor villaged. The location of the flag will possibly also show in the minimap as a small circle of the given colour.
4) The flag will slowly fade out after a while (something like 20-45 mins?), possibly with a duration determined by the placing chars sqrt(Cha)
You can at any point place a new flag, thus erasing your old one.
5) You have a toggle (default on) in the adventure menu to see or ignore flags.
You can not attach a lasting message to the flag (other than hint at the flags significance in a chat), nor is the flag an actual physical object in the game world - the flag is merely a representation of your char pointing at a certain place, or describing a nearby location to another char.