I am in El Salvador and have found that the flag is not of the Secretariat for Central American Economic Integration (SIECA) but the flag of the Secretariat for Central American Integration (SICA). The Secretaría de Integración Económica Centroamericana (SIECA) is a subdivision of SICA. I went today to visit the building and has the flag flying in front of it and it says SICA in front of it.
There are some better images and detailed descriptions at Wikipedia.
Description of a flag from official site:
"The flag has navy blue background with SICA emblem in the center, the spheres do not have any name or acronym, the black spheres symbolize the four Systems, the words PAZ (PEACE), LIBERTAD (LIBERTY), DEMOCRACIA (DEMOCRACY) and DESARROLLO (DEVELOPMENT) written in black encircle the emblem. These colors were used in ODECA symbols; blue symbolizes unity, white symbolizes peace in the region, and green represents the natural resources."
And description of coat of arms:
"The coat of arms comprises an external circle in gold color with the words SISTEMA DE LA Integración CENTROAMERICANA (CENTRAL AMERICAN SYSTEM INTEGRATION) and the SICA acronym in the lower part. These words encircle a round area in green that contains SICA scheme.
The map of the Central American Isthmus in blue is on the scheme on a green background; the concentric circles are in gold color. A partial silhouette of a white circular area in the center of this scheme, surrounded by green and behind a blue map.
Spherical golden figures of various sizes in which the acronyms are written, on the concentric circles.
The four biggest spheres located at the cardinal points symbolize the sub-systems of the economic, social, cultural and political integration; the medium-size spheres linearly interconnected symbolize SICA bodies; and the smallest spheres near the outer concentric circles symbolize the regional institutional organization and their interrelation. The coat of arms is encircled by the words written in golden letters: PAZ, DEMOCRACIA, DESARROLLO Y LIBERTAD (PEACE, DEMOCRACY, DEVELOPMENT, AND LIBERTY)."
It should be noted that the Wikipedia clearly shows the Dominican Republic on the flag, so this is a later version of the flag as the DR only joined as an
associate member in 2003. Belize was admitted in 2000, possibly it may not have been on original version of the flag either.
Flag and coat of arms of SICA (Sistema de la Integración Centroamericana) after the Dominican Republic joined in 2013.