The product owners wear multiple HATS in during their role, hence, there can be many titles which they can write on their business card. As they are the owners of a business or the product, the best-suited title can be similar to the highest ranks we have in an organization, like Product Captain, Business Marshall, Product Magnate. The product owners create a vision for the TEAM and help them walk the path towards attaining the desired goal, hence, the title can even be a Visionary, Servant Leader or Goal Keeper. 

They are often aligned with the strategic DESIGN of the roadmaps which makes them a Strategic Thinker or System Thinker. With the product development, the backlog over a period of time gets some in innovative ideas from the product owner which are liked by the clients too, and even the team works on them for launch, in such a case the title can be of an INNOVATOR. There can be several titles a product owner can have on their business card, it all depends on how creatively a person can think of.