As a community service, the Postal Service™ offers pictorial postmarks to commemorate local events celebrated in communities throughout the nation. The recent launch of the America the Beautiful Quarters® Program coin honoring Saratoga National Historical Park by the US Mint included a pictorial postmark. The Postmark is available for 30 days from November 17. You can mail your request (see below) to the AMERICA’S BEAUTIFUL NATIONAL PARKS Station, Postmaster, 25 Ferry St., Schuylerville, NY 12871-9998, Nov. 17. The postmark is described as an American flag, trees, stars around design of Saratoga National Historical Park commemorative quarter, which includes two hands, sword hilt. (The images above is from an earlier postmark and the Saratoga Quarter.)
Those who wish to obtain the postmark may submit a mail order request. Pictorial postmarks are available only for the dates indicated, and requests must be postmarked no later than 30 days following the requested pictorial postmark date.
All requests must include a stamped envelope or postcard bearing at least the minimum First-Class Mail® postage. Items submitted for postmark may not include postage issued after the date of the requested postmark. Such items will be returned unserviced.
Customers wishing to obtain a postmark should affix stamps to any envelope or postcard of their choice, address the envelope or postcard to themselves or others, insert a card of postcard thickness in envelopes for sturdiness, and tuck in the flap. Place the envelope or postcard in a larger envelope and address it to: Pictorial Postmarks, followed by the Name of the Station, Address, City, State, ZIP+4® Code, as listed below.
Customers can also send stamped envelopes and postcards without addresses for postmark, as long as they supply a larger envelope with adequate postage and their return address. After applying the pictorial postmark, the Postal Service returns the items (with or without addresses) under addressed protective cover.
This description comes from https://about.usps.com/postal-bulletin/2015/pb22420/html/info_010.htm another set of instructions can be found here.