This is a tuffy. A drone, even a small one, falls into the category of aircraft. Specifically, in the case of a drone, it's an Remotely Piloted Aircraft System (RPAS).
An RPAS must follow all the airspace rules of other aircraft but, because private drone operators are not trained pilots, they will be unaware of the regulations.
Uncontrolled airspace (Class G) doesn't require any clearance from traffic control and visual flight rules apply. But, without a detailed airspace map, and the ability to read it, you have no way of knowing if you are or are not in Class G airspace.
Flying into controlled airspace without a clearance is an Airspace Infringement (AI) and drones do it all the time.
According to FARs, you are required to use a Mode-C transponder, a device that broadcasts an unique ID and your aircraft's altitude even when flying in Class G airspace above 2500 feet Above Ground Level (AGL).
A transponder on a drone would also alert air controllers to the presence of a drone in the airspace (a small drone, made mostly of plastic, wouldn't be visible on most air control radars).
I would think this is an example of aircraft regulations catching up with technology. Trying to keep everyone safe.