Austria issued Scott 558 in 1948 to commemorate the 130th anniversary of the composition of the Christmas carol "Silent Night, Holy Night." The stamp features the tune's composer and the lyricist, Franz Gruber and Josef Mohr. The background design may be intended to represent organ pipes. Instead straight, erect pipes, they are curved or undulating, but the design does seem to include pipe mouths.
Mohr had composed the lyrics of the carol in 1816 when he was in Mariepfarr. In 1818, now living in Oberndorf, he asked Gruber to compose a melody and guitar accompaniment. There is plenty of folklore about why guitar accompaniment instead of organ; we'll likely never know the facts surrounding this choice. The song was first performed at a midnight mass on Christmas Eve 1818. The St. Nicholas Church, site of the first performance, no longer exists as it did originally. A memorial church stands in its place.