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 in chandeleer in Westerkerk
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, with 3 saltires