Markers are fairly cheap to craft, requiring only four planks and one wool. The wool is placed in the center with the planks in a plus shape around it.
Marker blocks have many uses that allow golems to be used for more complicated tasks. Stone golems can be made to place items into marked chests of a specific color. A common use of Markers is to show Tallow Golems where to get water, where to obtain empty phials and where to put full phials.
Note: Warded jars can be marked to have tallow golems fill them automatically.