In an opinion (which I'm having a lot of fun reading) by a three-judge panel of the [[United States Court of Appeals for the Eleventh Circuit]] striking down the use of mass metal-detector searches at protests, Judge Tjoflat referenced [[Homeland Security Advisory System]].
http://www.ca11.uscourts.gov/opinions/ops/200216886.pdf
From page 16:
"Although the threat level was 'elevated' at the time of the protest, '[t]o date, the threat level has stood at yellow (elevated) for the majority of its time in existence. It has been raised to orange (high) six times.' Wikipedia, Homeland Security Advisory System, available at http://en.wikipedia.org/wiki/Department_of_Homeland_Security_Advisory_System (last referenced Aug. 16, 2004)."