The SSSS mark is also handed out when you purchase your ticket shortly before the flight or when you pay in cash, or at the discretion of the airline. I've endured it more times than I care to recall because I frequently change my travel plans.
Looking at those criteria, it wouldn't flag terrorists who were well-funded, forward-planning, and punctual. Which sounds like prerequisites for a successful attack.
http://en.wikipedia.org/wiki/Secondary_Security_Screening_Se...