I've heard that RED, if they ever raise it that high, will be martial law, no unauthorized travel, etc.
5. Severe Condition (Red). A Severe Condition reflects a severe risk of terrorist attacks. Under most circumstances, the Protective Measures for a Severe Condition are not intended to be sustained for substantial periods of time. In addition to the Protective Measures in the previous Threat Conditions, Federal departments and agencies also should consider the following general measures in addition to the agency-specific Protective Measures that they will develop and implement:
Increasing or redirecting personnel to address critical emergency needs;
Assigning emergency response personnel and pre-positioning and mobilizing specially trained teams or resources;
Monitoring, redirecting, or constraining transportation systems; and
Closing public and government facilities.
I must be missing the mention of Martial Law.
Note to self - find the nearest gun shop to home and purchase a firearm - POST HASTE!!!!