2015 American $1 Coin & Currency Set - 9/11 Tribute. Bill Has 911 Serial #. Price is for 2 sets which are sequentially numbered. The coin has an enhanced finish and bears a W mint mark with a mintage under 89,000. For comparison, P and D mintages in regular finish for this year were over 2,000,000. A great 9/11 20th Anniversary Tribute which also has good investment potential based on low mintage.