Cool. I believe NAC 293 is the default Motorola NAC code, many APCO 25 ham repeaters use that because its the standard from what I remember.
Actually 293 is like the carrier squelch of NAC codes. In the early versions of the astro saber RSS NAC 293 would put the radio in to Digital Carrier Squelch, letting the radio here any digital transmissions regrdless if the right NAC code was programmed.
when you program and Astro Saber or XTS3000 for Digital Carrier Squelch it defaults to NAC 293.
Newer ASTRO25 radio's use F7E as the default for digital carrier squelch of the "hear all NAC".
http://batboard.batlabs.com/viewtopic.php?f=10&t=74854&p=343704&hilit=NAC+293#p341170