The 3 saltires (in Dutch 'Andreaskruisen') appear on Amsterdam's coat of arms. The origin of the crosses is unknown.
The 3 crosses have, on themselves, become a symbol of Amsterdam and are widely used on all kinds of objects.
Amsterdam coat of arms, with 3 saltires
Three saltires (crosses), symbol of Amsterdam
Amsterdam coat of arms in Sint Nicolaas church
Bicycle tunnel Amsterdam Central Station; Andreas crosses in war ship
Amsterdam coat of arms in chandeleer in Westerkerk