I'm about to begin construction on a Part 15 HiFER beacon. I was wondering what the guidelines are for picking a callsign. I would like one of these two:
MMI - Problem is this is an NDB in Tennessee, or somewhere around there
FFZ - This WAS an NDB at Falcon Field (FFZ) but has since been removed from the airport (online directories are still showing it in service)
Would it be taboo for me to steal an NDB callsign? I would hate for someone to confuse my beacon with the FFZ NDB and put their plane down on the US60.

But really, I'm struggling coming up with a good one... Bear in mind, I'm looking for something that sounds good in morse code so not "any" combination of letters will work for me.
Thanks,
Benjamin