<a href="https://en.wikipedia.org/wiki/Precancel" class="extiw" title="en:Precancel">Precancels</a> of Cristobal, the U.S.A. Panama Canal zone, 1928
<a href="https://en.wikipedia.org/wiki/United_States_Post_Office_Department" class="extiw" title="en:United States Post Office Department">United States Post Office Department</a>
own collection