This official Mayfair promo expansion was included as a retail give-away on a tile sheet titled: Limited Edition Promo Expansion Set #5. It is now also bundled with Steam: Map Expansion #5 The expansion consists of five city growth markers on five colors. They can be used instead of normal grey city growth markers. You place one of these markers onto the city when using City Growth action. Now this city has a one-time demand for that color cube. When one cube of the marker's color has been shipped to the city, the marker is flipped, which then acts the same as a normal city growth marker.