I recall that there was a costuming error with Tuvok early on in the show. The rank he was called and the rank he wore were not the same.
The separate insignia make sense from a creative standpoint since we as the viewer can see how characters from the two crews interact with each other, theoretically, without the cliqued, "You're so maquis!" and "you're so starfleet!" being yelled at the start of every scene.
Canonically, I'd imagine the maquis would have wanted to maintain some semblance of their organizational pride. It's not easy to throw off your uniform (or lack thereof) and pick up your enemy's.
Originally Posted by Emh:
"The Dutch don't count."
Originally Posted by Ominous Squirrel
: "Actually, we do: een, twee, drie, etc"