The Sign is a craftable Structure. While it can't be written on, it shows up as an icon on the map. As such, it can be used as a marker for areas of interest which don't show up on the map (such as Blue Mushrooms and/or Mushroom Rings, or Beefalo herds).
The Sign requires 1 set of Boards to craft and a Science Machine to prototype. If it is destroyed, the Boards are returned, allowing the player to build a new Sign elsewhere.
Don't Starve Together
In Don't Starve Together, Signs can be written on after being placed, much like the Directional Signs. When writing on a sign, the dialog will give the option to cancel, generate random text, or write to the sign. The text box can also be selected and typed into. There is no restriction on who can write or what can be written on them, but they can only be written on once. When examined, the character whose player examined it will say what is written on the sign. When the sign is burnt, the character will say something about it being burnt, thus losing its written information.