Unspecified, so legally murky. But there's a notion of "implied license", so someone using the code could argue that "openly putting it somewhere publicly" constitutes and implicit license grant.
Note by the way that you are ALREADY explicitly granting some rights by putting it on GitHub:
We claim no intellectual property rights over the material you provide to the Service. Your profile and materials uploaded remain yours. However, by setting your pages to be viewed publicly, you agree to allow others to view your Content. By setting your repositories to be viewed publicly, you agree to allow others to view and fork your repositories.
Arguing that this constitutes an implicit license to use this code probably wouldn't be too hard. However trying to relicense/redistribute is less likely. In the end this will have to be decided by a judge in court.
Note by the way that you are ALREADY explicitly granting some rights by putting it on GitHub:
We claim no intellectual property rights over the material you provide to the Service. Your profile and materials uploaded remain yours. However, by setting your pages to be viewed publicly, you agree to allow others to view your Content. By setting your repositories to be viewed publicly, you agree to allow others to view and fork your repositories.
Arguing that this constitutes an implicit license to use this code probably wouldn't be too hard. However trying to relicense/redistribute is less likely. In the end this will have to be decided by a judge in court.