School' Supplementary Plate - Post Mount Diagram 546 R2/RA2This permanent sign supplementary plate reading School should be used on roads where children are crossing frequently to get to or from a school. An alternative to this supplementary plate is the Patrol sign 547. 1. This sign warns drivers that they should anticipate that children may be present in the roadway, and therefore take a little bit of extra care with their driving. The supplementary plate can be supplied with the text in a variety of sizes