It actually stems from the old telegraph days, which is correct from what cknizeski posted. It just carried over and became common language.
Metro-Dade? In Florida uses "Q" codes that hams use
Rocky Mountain states use "break" often which carried over from many former military who went into public safety
Ohio, Indiana areas you will hear "ok"
California "Copy that"
Most started from old communication techniques and traditions and have evolved regionally based on the regional customs.
As a NY example, if you said "DMV" over the radio troopers will think your referring to the Department of Motor Vehicle vs Disabled Motor Vehicle heard in MA/CT (vs just DV for disabled vehicle).
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