One of my favourites (some of my American colleagues thought it was a compliment when I put it in the comments box on company circular reports! Until they found out what it stood for!)
What a load of b*****ks!
The author relates the tale of the police undercover units brought in to infiltrate in pit villages and originally monickered Fast action Response Teams before being quickly renamed Territorial Support Groups
Oxford confirms that there's no such word as "oan", and unless you can persuade people to start saying it as as a single word rather than as a string of letters, it's not an acronym. I suspect it's unlikely to take off as a true acronym since "oan" as a word looks like it would be far too easily confused with "own".
Turdus torquatus' alternative suggestion would be a true acronym.