Here is the 15 groszy value (Sc #322) from Poland's November 11, 1938 "20th Anniversary of Polish Independence" set of 13. Stamp depicts King Ladislas II Jogaila (1357-1434) and Queen Hedwig, a.k.a. Jadwiga (1374-1399) with a prelate.
From oxfordreference.com, "King of Poland (1386-1434). He was grand duke of Lithuania from 1377 to 1401, during which time he was known as Jogaila, and acceded to the Polish throne on his marriage to Queen Jadwiga (1374-99), thus uniting Lithuania and Poland."