Thanks to jberlin for the following.
The photo of the Island in Ms Hawking's laboratory captioned "9/23/54 U.S. ARMY - OP 264 TOP SECRET - EYES ONLY". The date in the caption is in the wrong format. The U. S. military, especially the Army, uses a day-month-year format, so the caption should actually read: " 23 SEP 54 U.S. ARMY ...".
References:
http://www.olive-drab.com/od_time_24hr.php
http://answers.yahoo.com/question/index?qid=20071129193757AAtrChY
http://en.wikipedia.org/wiki/Calendar_date