I am not particularly observant so I often don't notice things until I suddenly do. This morning I became aware of an odd artefact at the top of the Geekzone page. This is not caused by my display. It is specific to Geekzone and only shows when the page is scrolled up to the black area at the top, above the links in yellow at top right.

What I see is faint green vertical lines extending across the display. The lines appear to be made up of pixels that are rapidly flashing off and on, giving the lines an appearance of vibrating motion. It is quite possible this has existed as long as Geekzone has, but I only noticed it this morning. Is it supposed to be some kind of decorative effect?

I just tried a screen capture which I saved to a jpg. I still get the dancing lines on the static image. What on earth is this?