I don't think it's been identified. However, she is a long-serving Starfleet officer, and was both a Chief Fleet Inspector and a (probably senior) instructor at Starfleet Academy before joining the Enterprise, so you could make a reasonable guess that it's a badge of seniority/advanced qualification.

It was...okay. I liked what they did with Seven getting the hang of Starfleet. But the main plot was just the usual Big Villain Apocalypse Drama. Oh boy, another end of the Federation threat! And it's the same one we had the last two seasons! I wish they would've got away from everything being on fire all the time and done a lower-key story with more room for the characters to be themselves.