The following is usually used in PHP: MyNamespace\Foo::bar()
Edit: Reply to comment
Since static methods can be called dynamically, you could use MyNamespace\Foo->bar()
to cover for both cases. However, standard usage I've always seen across all documentation, and usage that IDEs can generally recognize in docblocks when you ctrl+click through them all seem to be with double-colon, as originally noted.
I haven't seen Doctrine's approach in many cases.