I found some blog posts about pixel rulers for Visio. It seems that folks wanted to dimension their Visio shapes in pixels, which Visio doesn’t technically support by default.
But for folks who use Visio to do web-layout wireframes, information architecture and storyboarding, pixel-dimensioning is a useful thing to be able to do!
An earlier article on Visio Guy served up the Rack Unit Dimension Line, which can actually be configured to measure shapes in terms of pixels. But to save time, I’ve modified that shape and offered it here, for your pixel-dimensioning enjoyment.