This is about Kingdom: New Lands
The signpost is a naturally generated structure found deep in the forests. The Monarch may "buy" the map hanging from it for two coins, starting the unlocking process of a new feature for future Kingdoms.
This new feature is successfully unlocked and revealed only at the end of the current Kingdom, either through escaping to new lands or being defeated by the Greed. The unlocked feature might appear the next time the Monarch gets shipwrecked. Restarting the game (pressing New Game at the map menu when pausing) will not conclude the unlocking process, and the Monarch will have to pay for the signpost to start the unlocking process of the same feature once more.
The upgrade that a signpost unlocks is randomly selected but constrained to the possibilities of the island it's on and each feature can be unlocked only once. Once all upgrades on an island have been purchased, the signpost can still appear in the forest but without a map attached, and it cannot be interacted with.
For details about each islands' unlockables, see Islands/New Lands.
For example, the second island has three features. To unlock them all, the Monarch has to shipwreck there and pay for the map three times. To be sure these three features have all been unlocked, in all future visits to this island, the Monarch will find the signpost with no map.
|1st||Statue of Archery|
|2nd||Statue of Building · Dog · Superior horses|
|3rd||Statue of Scythe · Ballista Hermit · Stag|
|4th||Statue of Knights · Bakery Hermit · Warhorse · Bear|
|5th||Knight Hermit · Unicorn|