Currently you can use 3D markers that look like billboard markers.
In this case, you will have full control of the rotation of the markers.

Thanks Alex.  I'm wondering what's the easiest way to leverage this idea.  That is, does online maps have a  component/class  for achieving billboard marker via my 3D Marker game object or is this purely unity implementation.

Anyway, just thought I'd ask before I go about doing things the hard-way LOL.

EDIT:  I solved this by using a Quad game object and sprite/texture shader

Unfortunately, in the current version of Online Maps you can not add additional rotation for billboard markers.
If you need this feature, we can add this.

Currently you can use 3D markers that look like billboard markers.
In this case, you will have full control of the rotation of the markers.

OnlineMaps.instance.AddMarker(lon, lat, null, name);

For my project and my camera, the rotation of these 2D markers is not allowing me to see them.  I'm seeing the billboards from the top, and I need to rotate them 45 degrees (on the Z i think). Can you tell me how to rotate them via code? 

Thanks.