In 1964, the United Arab Republic (only Egypt, as Syria left the union is 1961), issued a series of 13 stamps with the flags. Each stamps featured the flag of one of the Arab countries that formed the Arab league then . Below is the Saudi Arabia flag postage stamp.
The stamps with flags were issued on the occasion of the Fourth Arab Summit, that gathered in Alexandria, Egypt on September 4, 1964.
One of the most important decisions of this summit was to welcome the establishment of the Palestine Liberation Organization (PLO), created by the first Palestinian National Council, held in Jerusalem in May 1964.
The stamp above bears the flag of the kingdom of Saudi Arabia.
The kingdom of Saudi Arabia was declared by king AbdulAziz Al-Saud in September 1932. It was one of the 7 founding states of the Arab League.
Yvert & Tellier: United Arab Republic YT-612d