Use of a white cross as a mark of identification of the combined troops of the Old Swiss Confederacy is first attested in the Battle of Laupen (1339), where it was sewn on combatants' clothing as two stripes of textile. Civilian use of the white cross as a symbol of the confederacy is attested from the 16th century. From the 17th century, the white cross was carried on the banners of all cantonal troops, on the background of the cantonal colours.
source: wikipedia