Been around for quite a while. Usually they call it Channel 2; its official name is Mainline Ops 2. While we're on the subject...
60048 Mainline OPS 1
60080 "OPS 2" "Channel 2"
60112 "Channel 3"
60144 Yard Ops
60176 Light Link "Channel 5"
60208 (Would be Channel 6)
60240 (Would be Channel 7)
60304 Bus Tunnel Security
60368 (Would be Channel 11)
60304 has been around for a long time. I've caught traffic a few times on 3 and 5 and heard them call it "Channel 3" and "Channel 5" but nothing else. "6" & "7" they've never referred to a channel name. I only call them 6 and 7 because based on the spacing, that's what they'd be. 3, 5, 6, and 7 seem to be used by the contractors only. On 5 I've heard a lot of two guys setting up the various surveillance cameras. "11" I've only seen once--"___ we're in the yard now." and about 4 minutes later "Train 3 to LCC". LCC=Link Control (Center?). You can see Link Control 1:09 into
this video.
And in case you're wondering--LINK Light Rail is scheduled to open July 3, though it's rumored that it might be later because "the City of Seattle asked Sound Transit 'not to have their opening on the 4th of July weekend'."