Jade Coins are a currency in Samurai Siege.
They can be spent to build and upgrade defenses, build and refill traps, build and upgrade walls, and to pay to search in multiplayer battle matchmaking. They can be collected from Markets and by attacking other players' villages. The level of the market increases the hitpoints, hourly rate of collection and overall collection limit of the Market. Upgrading the market will allow you to leave the Market overnight without it filling up and becoming an easy target for raiders.
The Jade Coin's shape reflects actual ancient currency from the far east.
A symbol for the jade coin can be found on the awning of the Market, especially noticeable on higher level markets.