I found prior flight data for the type DHC6, Callsign ANVIS, Registration 82-23836, out of Davison Air Force Base.
It flew a strikingly similar flight path on
11/30/18 https://flightaware.com/live/flight/ANVIS/history/20181130/1423Z
12/3/18 https://flightaware.com/live/flight/ANVIS/history/20181203/1424Z
and 12/4/18 https://flightaware.com/live/flight/ANVIS/history/20181204/1609Z
Pics 1,2,3. Look at the altitude profile though! I'm not a pilot but find it difficult to believe it could have actually traced that path in the air with those precise altitude changes. Maybe it did; or maybe the transponder was purposely programmed to emit those altitude signals. Low & slow.
No registration or photos found for 82-23836 on Flightaware.
Pic 4. https://flightaware.com/photos/aircraft/8223836
This aircraft is operational according to https://www.twinotterworld.com/msn-801
and received its current registration # when delivered to its 3rd owner, the U.S. Army- Alaska Air National Guard on March 11, 1983.
I am inclined to think this unusual flight path has something to do with its mission and a bit less inclined to think it's a special signal to anons. But it might be. Did it take 4 flights to get our attention? Last time it flew while AF1 (w/o POTUS on board) was up and anons were tracking AF1.