Marker seeds are used to plant Marker plants, similar to the way mithril seeds are used to plant flowers. They can be planted in most areas and can only be removed by the player who placed it there. They can be bought from Faruq's Tools for Games in Al Kharid for 65 coins each. The bag of marker seeds can plant an infinite number of marker plants, but the plants can not be planted within 10 squares from another, and has a 10 second cooling time before another can be planted.
The seeds can be simply planted to mark a spot, or can be made to point north, south, east, west, north-east, north-west, south-east, south-west, or the player's current direction. All players can see the plant indicating direction if shown. Your marker plants are temporary and are destroyed after six minutes, or when you log out. Players can use the plants to mark out paths or trails to follow. Other players might plant Marker Plants to confuse that path. However, the 10 square distance limit applies to all players planting marker seeds.