As a senior PMM with 8 - 10 years of experience under my belt, how do I position myself for a Director/Head of Product Marketing role without direct report experience? Besides people management skills, what other skills can a candidate highlight to stand out from the candidate pool?

IMHO, the jump from Senior PMM to Director/Head of PMM is one of the biggest! Having people management skills is important, yes, but it's not the only skill that's needed at that level. It's critical to be a strategic leader - this means aligning initiatives with business objectives. You've got to have a proven track of cross-functional collaboration and driving results. To do this, the best PMM directors I've seen are data-driven, adaptable, and they think outside-the-box - always thinking of new ways to do something and innovate. Of course, you must also be an expert in your market/domain; in fact one way to stand out is through thought leadership. (By the way, even if you haven't had direct people management experience, you can highlight any dotted-line and mentorship experience!)