The XXX symbol is three St. Andrew’s Crosses in white on a black stripe on a red background.
St. Andrew was a fisherman who lived in the 1st Century AD and was said to have been crucified on an X-shaped cross. The Amsterdam XXX symbol dates back to the year 1505 when the city was a fisherman’s town, so the coat of arms was established as the symbol for the city itself and it also flew as a flag on all ships registered in Amsterdam.
ABC Wednesday
signs, signs
above photo taken from this sign for the Amsterdam Bridge on the waterfront in Toronto
you may need to click on sign to embiggen if you want to read it