On October 5, 1938, a decree of the German interior ministry invalidated every passport held by a Jew in the Reich. Holders had to hand them in within two weeks, and any new passport issued to a Jew had to be marked with a letter J large enough to be obvious. The regulation took effect on January 1, 1939, and it covered the whole population classified as Jewish under the Nuremberg Laws of 1935, about 350,000 people in Germany itself.
The request came from Switzerland. The Swiss had been alarmed by the numbers entering after the Anschluss in March 1938, and they proposed that Germany mark the documents of its Jewish citizens so that border police could refuse them without argument. Berlin agreed, and the negotiations over the design of the stamp were conducted by the Swiss police division and the German interior ministry through the summer.
What made the measure bite was that a passport is more than a travel document. Jews in Germany had already lost the vote in 1935, had been driven out of most professions under the Nuremberg Laws and the decrees that followed, and had been pushed out of the civil service in 1933. Without a valid passport a person could not leave, could not take money out, and could not get a visa, since most consulates would not issue one against an invalid document.
The autumn escalated anyway. On October 28 the government deported about 17,000 Polish Jews living in Germany to the border, and Poland refused to take most of them, which left them in camps at Zbaszyn for months. Herschel Grynzpan, whose parents were among those deported, shot a German diplomat in Paris on November 7, and the killing was used as the pretext for Kristallnacht on November 9 and 10.
Emigration was still policy. About 300,000 Jews left Germany and Austria between 1933 and 1939, most of them after this, and where they could go was the problem the stamp had been designed to help create: the Evian conference of July 1938 had produced no country willing to take substantial numbers. The J in the passport is what made refugees identifiable to every border official in Europe.