Comment053977 is in a reserved ICAO 24-BIT range : "tactical" NATO. We've seen it used once before little over a year ago by a Luxembourg/NATO Sentry in the very same area : LX-NXXXXX.
LX-N90456, a Luxembourg/NATO Sentry turns up today over Constanța.
Like then a Turkish K35R was in the area too : ASENA21.