Either the source itself, or a written offer to provide the source. But you're right that 'vaguely gesturing' at it doesn't seem to be permitted. Not to mention

Either the source itself, or a written offer to provide the source. But you're right that 'vaguely gesturing' at it doesn't seem to be permitted. Not to mention the license terms not being prominent in the binary (with hardly anyone outside of GNU actually putting a license command into their programs). This kind of stuff is why I'm not in the business of distributing free software.