U : Unclassified, S : Secret, SI : special intelligence (an SCI control marking), REL : marking that designates release There's a bunch more too: http://en.wi

U : Unclassified, S : Secret, SI : special intelligence (an SCI control marking), REL : marking that designates release There's a bunch more too: http://en.wikipedia.org/wiki/Classified_information http://en.wikipedia.org/wiki/Classified_information http://en.wikipedia.org/wiki/Sensitive_Compartmented_Information http://en.wikipedia.org/wiki/Sensitive_Compartmented_Informa...