SAN SALVADOR
Double Oval "Admon. jral de Corr. de Est. /  SAN SALVADOR" in Black
1800 - 1818

Used With Red "FRANQUEADO" in Fancy Frame
Marking also exist in black.

ADDRESSED TO LA UNION
Double Circle "SAN SALVADOR / SALVADOR" in Black
1862 - 1865

Used With Fancy Framed "FRANCO" in Red.

1865 APRIL 5: ADDRESSED TO NEW YORK
Double Circle "SAN SALVADOR / SALVADOR" in Blue 
1866

Used With Fancy Framed "FRANCO" in Blue.

1866 JUNE 20: ADDRESSED TO NEW YORK

UNLISTED IN BLUE COLOR
Black "FRANQUEADO / EN S. SALVADOR" in Oval

ADDRESSED TO GUATEMALA

ONLY KNOWN - DISCOVERED IN 1995