I know Roll20 is more for RPGs but I like to try miniatures on here as well. I'm playing "What a Tanker!" which is a WWII tank combat game. I needed to rotate the turret and have it stay in that position even when I move or rotate the tank. You can hide the LOS marker, rotate the tank around and the marker stays in the correct facing. Then unhide it and you can see where the turret is facing.
Borrowed heavily from TheAaron's Facing script.
Here's the link to github:
https://gist.github.com/littlebigbucky/07995e9b91d23a26ff2aa929a86f1e2d
Click on gif below to see example.