Product marketing is a relatively new function so this is a question I get a lot.
A great way to help companies undestand the PMM function is by helping them understand the value of product marketing. There are all sorts of way to establish value. One place to start is by clearly defining what you and your team's contribution will be (which should map to the overarching business goals) and then delivering against those goals.
Socializing your team's stated goals and objectives with internal roadshows could be your first step in helping the organization understand the PMM role, responsibilties, and objectives. Once you've established and socialized your goals, check back in with your organization (frequently!) when you have results and achievements to share. These results should show how your team delievered against the objectives you laid out in your intial plan and how your team has positively and measurably impacted the business.