Colored flags usually represent underground utility mark outs. If any digging is to be done in the area, the contractor, by law, must first call for a utility mark out. All the local utility companies will then come and mark the approximate location of their underground utility lines. Sometimes the name of the utility company is marked on the flag. Professional land surveyors also mark out property corners, or survey markers. They sometimes mark the proposed location of something that is to be constructed. These colored markings are ribbon tied to a piece of wood to signify the approximate location of the survey point.