Odd there is no tail number posted for this craft. According to the squawk it could be this: 5100, 5200, 5300, 5500 US Internal ARTCC subsets assigned by En Route Safety and Operations Support (Discrete codes only except for first primary block to be used as non-discrete if all discrete codes are assigned)[3] Or this: 5100–5300 US May be used by DOD aircraft beyond radar coverage but inside US controlled airspace with coordination as appropriate with applicable Area Operations Directorate[3]