As I have found out, there are "open-source hardware" licenses which are written in the spirit of "open-source software" licenses and require the user to publish a modified design if they distribute a physical product based on that design. Examples are TAPR and Arduino license.
However, unlike software which is subject to copyright in any form, circuit boards are not subject to copyright as they are not works of art. This makes me wonder whether open-source hardware licenses can actually provide the protection that they advertise.
Are such licenses deemed legally enforceable? Have they ever been enforced?