There’s no shortage of Pentagon postcards, but the Smithsonian–which should know better, we think–loudly captions this as being in Washington, DC, when of course it is across the Potomac River in Arlington.  Oh, well.  Mailed in 2013 with five different stamps (two of them uncancelled) and full postmark.  Perforated left edge suggests it came out of a book.  Grade: 2