No, it's not the long-lost final verse of "ICU," it's shorthand for the announcement that They Might Be Giants will prresent, "1,2,3... TMBG!," an "exclusive" XM Radio event hosted and produced by John Flansburgh and TMBG.
It'll air Friday at 8 PM, Saturday at 9 AM and 5 PM, and Sunday at noon. (All times Eastern. East Coast Bias, grr...)
I might be going out on a limb, but I think it has something to do with Here Come the 123s.