Yea I always wondered what that means. Is it always 5 lines?
Sorry, it's not just five, it actually looks like this:
IIII IIII IIII I
So it was actually sixteen. I was just describing the base unit of five, since I couldn't think of how else to describe it. And yes, it's always the same number of lines. it's part of the texture of the shield, so all imperial shields have it.