The answer is in this topic:
https://www.halowaypoint.com/en-us/forums/84ad72a8b51847978545f685f651fc15/topics/saw-something-strange/d8f356b3-05db-4c74-a97e-27a13e76b9c0/posts?page=1#post3
You can earn this nameplate by playing Halo: Spartan Strike
