Nac code?

[apd3190]

I'm Monitoring a 380s frequency showing a nac of FFB. The wiki shows this as USSS however I was able to identify the units on the channel as military police from a nearby base. Any ideas on why ?

 

[sound_efex]

USSS = United States Secret Service

 

[nd5y]

You were probably picking up a voice channel from a military P25 trunked system.
Various systems and agencies use various NACs. Just because wiki article shows USSS uses a particlular NAC on a particular frequency at a particular location doesn't mean they are the only agency that can use that NAC.