Not only is it impossible to adjudicate or police, I feel like this will absolutely have a chilling effect on people wanting to share their projects. After all, who wants to deal with an internet mob demanding that you disprove a negative? That's not what anyone who works hard on a project imagines when they select Public on GitHub.
People are no more required to disclose their use of LLMs than they are to release their code... and if you like living in a world where people share their code, you should probably stop demanding that they submit to your arbitrary purity tests.