An identical sign can be seen during the fight sequence in the Circus railway carriage between James Bond [Roger Moore] and Mischka [David Meyer], one of the knife-throwing twins from the Circus.
According to the vendor, who was a Security Specialist with the U.S. Air Force, stationed at RAF Upper Heyford during the period of time in which the base was used as a shooting location for Octopussy, he...was appointed as one of the security escorts for the film crew. I was usually assigned to Mr. Roger Moore...
On completion of filming, the original owner was given the sign as a memento by the prop department.