1926 WHITE PLAINS SHEET SCOTT #630 AMERICA'S FIRST SOUVENIR SHEET

A commemorative honoring the 150th anniversary of the Battle of White Plains was issued in 1926 in a 100 stamp sheet. Later that year, a special 25 stamp sheet with a commemorative inscription in the sheet margin was issued with the same design for the International Philatelic Exhibition. This sheet became the first U.S. souvenir sheet that the Post Office produced.
  Interesting fact--only 107,398 souvenir sheets were printed over 85 years ago, so today they are very rare.