Knox Martin Air post issue. Key value, numerals "1" with Serifs. Few tiny toned perforations but defintively a FINE, VERY FINE stamp. With 2017 PF photo certificate. The item "COLOMBIA 1919 KNOX MARTIN AIR Sc C1a UNUSED WITH PF CERTIFICATE SCV$7,250" is in sale since Monday, November 20, 2017.This item is in the category "Stamps\Latin America\Colombia". The seller is "victorgg" and is located in Buenos Aires. This item can be shipped worldwide.