CEDA

CEDA (Civil Emergency and Defense Agency) is a fictional governmental organization in the Left 4 Dead universe. Materials with the CEDA logo advising Survivors can be found in numerous safe rooms.

Overview
According to descriptive text on Valve's store page for the CEDA Coffee Mug, CEDA has protected millions of Americans from the terrifying consequences of natural and man made disasters since 1988.

Involvement with containing The Infection
"Safety Checklists" with a "CEDA" logo have been spotted around the now-deserted Fairfield, instructing residents to barricade themselves in their basements and wait for help to arrive.

They also instruct citizens to seal their windows and all other openings with plastic sheeting and duct tape, implying an airborne infection. However, one sign in the safe room at the end of The Subway has been written on by another Survivor, saying "NOT AIRBORNE".

Apparently, the population is extremely dissatisfied with CEDA's safety measures and course of action, as implied by graffiti in the safe rooms of Crash Course and The Parish campaigns, which read as "CEDA BLOWS".

Superseded by the military
In Left 4 Dead 2, it appears that CEDA has been superseded by the military. A CEDA-run quarantine zone in The Parish has been closed and military-run quarantine zones can be seen throughout New Orleans. Also, CEDA-issued instructions on building a safe house demand that there be no guns in the safe house, but military-issued instructions on making safe houses encourage citizens to be armed.

It is likely that the military stepped in and took over because of CEDA's failures in Fairfield, Newburg and possibly Savannah in containing The Infection.

Trivia

 * CEDA appears to be based off of the real-life FEMA, especially in its advice to cover windows with plastic sheeting and duct tape.
 * The Infection Warning posters may be a reference to the Return of the Living Dead films, where the barrels always have the contact number "555-" but the rest is scratched out, much like the posters. (Note: the telephone prefix "555" is a commonly used fictional telephone prefix)