Sigmartag

This festival celebrates Sigmar's ascension to the heavens as a god. It also marks the first day of summer. Throughout the Empire, work ceases and citizens feast, drink, and sing. Sigmar's exploits are recounted in tales and plays. Consumption of the intimidating ‘Sigmar's sausage’ is central to the celebrations. Those who manage to eat a whole sausage in a single sitting are promised strength and vigour for the rest of the year.

The most magnificent celebrations take place at the High Temple of Sigmar, presided over by the Grand Theogonist, and attended by the Emperor. Thousands crowd outside the temple to partake in the holy liturgies. The festival culminates with spectacular pyromantics organised by the Bright College (though many priests of Sigmar boycott this display).

There are various holy days devoted to Sigmar throughout the year, marking events of Sigmar’s life such as the rescue of King Kurgan, the Battle of Black Fire Pass, and his coronation. Dwarfs, as the allies of Sigmar, are honoured on such festival days with gifts of food or drink presented to them by passing strangers.

A major festival in Altdorf marks the accession of the first Grand Theogonist, Johann Helsturm. On the 33rd of Sigmarzeit, Sigmarite priests parade Helstrum's gilded skull and his sacred mace through the capital’s crowded streets.

Source
pg. 30
 * Warhammer Fantasy RPG 3rd ED -- Signs of Faith