The non-profit St. Nicholas Center (stnicholascenter.org) hosts material “to educate people of faith, and the wider public, about the true St. Nicholas, and why he is important in today’s world”. Of interest to vexillologists is their page and database St. Nicholas in Civic Heraldry, which lists coats of arms of dozens of “cities, villages, towns, districts, churches, and other institutions” on which symbols of the saint appear.
One of the main symbols of Nicholas are three gold balls (or coins, or bags of money, or maidens). The story is that Nicholas surreptitiously gave an impoverished man three bags of gold so that his three daughters might have dowries. He threw these in the dead of night into the man’s house. One of these landed in a stocking hung drying by a fire, the basis of the Christmas tradition of hanging stockings for Santa Claus, and putting an orange (“gold”) in the toe of the stocking. (The three coins are also the basis of the three gold balls representing pawnbrokers, of whom St. Nicholas is the patron saint.)
These three coins — or bezants as they are known in heraldry — feature on many of the civic coats of arms listed at the St. Nicholas Center. Here are some examples (imagery from the Heraldry of the World website):
Portland Flag Association 