What is K9 ?
The term 'K9' or 'K-9' is derived from the English and French word 'CANINE' (which simply means 'DOG'). 'CA'='K' and 'NINE'='9' (same as 'YOU TOO'='U2').
The first use of 'K-9' goes probably back to 1942. In that year the first military K-9 Corps were created by US Secretary of War Robert P. Patterson. Later in 1959 the wordmark 'K-9' has been registered as federal symbol in the USA Trademark Office by the US Army. Since than the terms K-9 or K9 became commonly used for dogs in general, service dogs and working dogs.
Even in the cinema it became a popular theme:
-'Marvin the Martian & K-9' from Looney Tunes (1948) http://looneytunes.wikia.com/wiki/K-9
-'K9' English TV series with Doctor Who (1977) https://en.wikipedia.org/wiki/K9_(Doctor_Who)
-'K-9 Transformers' Japan (1984) https://en.wikipedia.org/wiki/Transformers_(toy_line)#Beast_Wars.2FBeast_Machines_Maximals_Toy_Characters
-'Rintintin K-9 cop' French/Canadian TV series (1988) http://www.imdb.com/title/tt0094491/
-'K-9' film with James Belushi (1989) https://en.wikipedia.org/wiki/K-9_(film)
and many more...
The Security, Rescue, Police and Army forces all over the world use the symbol 'K9' or 'K-9' on their police cars, on their clothing, on their patches and on their dogs. These K9 teams carry the name 'K9 unit'. 'K9' is also used for dog clubs, dog kennels, dog training, commercial dog items, etc.