Late to the party but for what it's worth:
HFGCS, and the entire 789th Communications Squadron, exists for command and control. Hence why HFGCS operators have the AFSC of 1C3X1 Command & Control Operations. While the traffic they handle is referred to on the internet as Emergency Action Messages, not all the traffic they handle are EAM's. It's a mix of headlines, phone patches, sitreps, commands, and of course...EAM's.
Most of the traffic are just routine commands or guidance for STRATCOM, REACH, or Exec air missions, all the way to surveillance missions. For example, those surveillance missions pushing the authority of China in international airspace over the South China Sea, etc. Then of course there's null messages to monitor propagation to a given receiver, there are sitreps for on-going tensions and world events, there are training messages. As many boring and routine messages as there are critical commands and time sensitive information.
That said, the length and frequency of repetition of a single message, or a series of messages, is in fact an indicator as to it's legitimacy or it's urgency. A 30 character message can be assumed to be routine depending on it's repetition. Over 40 characters should raise eyebrows. Over 0 you should sit up in your chair. Over 80 characters turn on the news, your favourite ADSB monitor, and wait.
Basically the same thing with Skyking, Skybird, or Skymaster messages. If the command word is a band on your iPod, it's probably nothing crazy. If it's a sports reference, cypher or Foxtrot message, it should get your attention. And it's not automatically for an E-6B either.
Just some stuff you learn when you've been into OSINT and HFGCS long enough, and have met people on the other side of the mic.