In some contexts its useful to have the Marker tag set to true for armor stands that are intended to be markers. I think create_marker() should set that. Main reason I've encountered is having the marker glow, so that it shows though walls. Doing that without Marker:1b results in the body of the stand also glowing, not just the block in its head.

well, funnily - that option was always there, just I never documented that in the API docs. This should cover that. I also adjusted the Y position for markers so it shows up properly.