This calls (pun intended) for another appearance by our legal ID
interpreter geek, Scott Fybush. (And I mean geek in only the
nicest sense, as I am one too.

)
Based on past threads about legals (not to be confused with
the "illegal power aliens" threads on the Phoenix board), if
WGBH is running the same programming on analog and HD1,
the legal ID--in its strictest interpretation--should be:
"WGBH Boston, WGBH HD1 Boston."
Some stations lump the calls first, then the COL, which seems
to pass Uncle Charlie's muster, based on the totally vague HD
ID rules they've published:
"WGBH, WGBH HD1 Boston."
As noted earlier, there is no "-FM" suffix in their callsign
(check the FCC FM Query), however this brings up the
question--since there is also a WGBH-TV, shouldn't the
FM need the -FM suffix? When there are common-called
AM and FM stations, the -FM is suffixed. Is there not
such a requirement when the calls are shared by FM/TV?
It is legal to add the frequency between calls and COL.
The alternate programming on the HD2, etc. channel(s)
would be IDed on those channels.