Regardless of any rules, if you think the turn signals are obscured from the side when using the bags, you may want to re-think the setup.
(Assuming you use the signals!)
Maybe you can mount some small turn signal lights on the side of the soft bags, and fabricate some easy wire harness/plug that would be discrete and hook up easily?
They wouldn't have to be large lights.....or stick out, just add some visibility from the side.
I'm anal about visibility....and rather add it, than remove it.
There's probably some low profile, LED lights out there that would work, be visible, and wouldn't look bad.