The reason the Adam Boy etc alphabet is used on TV shows and movies
about LAPD is the LAPD  has (maybe had) a detail to support the 
entertainment industry.  Therefore you see a lot of movies and TV shows
about LAPD that are pretty technically accurate.  On the other hand,
when they so a story about the police somewhere else it isn't.
For instance the CA light Package (one steady red light to the
front and flashing amber to rear) has never been used down here in
the south nor by NYPD but you will see it on TV.  DE AAR4LG\WA4MJF
Inspector, Enforcement Section NCDMV
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