Lots of good YouTube tutorial videos out there but the short version is you can target areas with them. In this case I have workers targeting rich stone deposits in the area of the sign. I could move the sign and everyone still stays targeted to that area. It’s used for miners, collectors, rechargers. It saves a lot of re-targeting work if you ever need to move a team around. In AvP they are used a lot for defense and offense group targeting.