[Aoi Kurenai]

Gaim's are represented by the blue lines that meet up with the eyes, Double's by the black triangles at the corner, the bottom half of the silver lines on Wizard's face are his tear marks and Decade's bar codes serve as his. The tear marks are a little different in every design, mostly to remain stylish, but they're there. Fourze's producer in an interview made it a point to declare that Fourze would be the first Rider with no tear marks until his eventual power up came along.

But yeah, the tear marks most definitely were originally just a way to explain the holes in the helmets. Over the years they've sort of just evolved to become part of the iconic look of a Kamen Rider though. (especially these days when there are so many ways around having them)