Only schools (K thru college) are listed in MGLs at least in one place. There is at least a CMR on Logan Airport Security Zone.
Federal buildings are not a MGL issue, but whatever Fed Law says. The answer on the USPO is "inconclusive" as USC allows "legal purposes" but CFR INTENTIONALLY says otherwise, rumor has it that the Feds have prosecuted on this, but nobody can cite any cases involving customers (one cite is a an employee, but that's not the same thing) "just gong about their business".
MA Courthouses . . . not actually per MGLs, more a directive from chief justices of each court. For example there is no sign and no security at all in two County Land Courts that I've been in in Southeastern MA.
If you see signage (in a gov't bldg), metal detectors, x-ray machines, etc. just don't carry in there no matter what the building is (e.g. Boston City Hall, 1 Ashburton Place, some other state office buildings, etc.). Most city/town halls don't have any of this stuff, but a few do.