This is an Interpex cachet – used at the United stamps exhibition, 04 July 1965. It has the Salvation Army stamp on it, but sadly, it is not an FDC as the stamp was issued only two days earlier. There is also a cindarella stamp “Fight Communism” attached on it (this was some years after the McCarthy period).
A new set of stamps was issued by Sierra Leone in June 2020. The stamps commemorate the 155th Anniversary of the Salvation Army. The Salvation Army “opened fire” in Sierra Leone i 2010. The stamps are produced by an agent who releases commemorative stamps on behalf of the government as a mean of gaining revenue from collectors. As they have official permission, it is a genuine issue. However, these stamps will likely not appear in any post office in the Sierra Leone itself.