Cita APA (7th ed.)
Associated Collectors of El Salvador & Freer, B. P. El Salvador Postal Stationery Handbook: Section 1 - Postcards.
Cita Chicago (17th ed.)
Associated Collectors of El Salvador i B. Phillips Freer. El Salvador Postal Stationery Handbook: Section 1 - Postcards.
Cita MLA (9th ed.)
Associated Collectors of El Salvador i B. Phillips Freer. El Salvador Postal Stationery Handbook: Section 1 - Postcards.
Atenció: Aquestes cites poden no estar 100% correctes.