I asked support about this mark back in 2016 and they said the mark is not available in the game. Nor did they know if or when they will implement this mark to the game. It is a beautiful mark though. As of March 20th, 2019 (when I opened the marks window), the Guardian Angel Mark and placeholder spot has been removed. So I'm guessing it won't be coming any time soon or it will be linked with some sort of event or purchase.