MUTCD S5-1 School speed limit when flashing sign.
From: Manual on Uniform Traffic Control Devices for Streets and Highways - 2003 Edition. Category:Diagrams of road signs of the United States
Any traffic control device design or application provision contained in this Manual shall be considered to be in the
public domain
. Traffic control devices contained in this Manual
shall not be protected by a patent, trademark, or copyright
, except for the Interstate Shield and any other items owned by FHWA.