Perimetr. Dead Hand.
Not likely. There aren't enough bits in the transmission to authenticate the transmitter. The buzzing noise is mechanically generated and picked up by a nearby microphone. This is not a secure system by any standard; you could destroy that one, play back the taped recording from years earlier, and nobody would notice.
Perhaps this is simply an indicator of some not every important system, since it can be paused and resumed at will. Maybe it is an old RF propagation monitor, given the shortwave frequency. Though a carrier wave or a slow FSK, like WSPR, would be more suitable for the purpose.