"Watermark" is a word most people in the desktop publishing arena are familiar with; it refers to a figure or design impressed to the paper and always visible in the background. In web design terminology, a watermark background image is very similar in concept to a paper watermark. It refers to an image that is statically positioned in the background of the document, and always visible (even when the user scrolls the page).
In the past, you may have used the bgproperties attribute of IE 3 to create a watermark. The problem with this attribute is that it tiles the watermark image if it does not fill the browser screen (like any background image), so in order for the effect to be successful, the size of this image has to be nearly as large as the screen.
In IE 4 and NS6, CSS can be used to create a watermark background that does not tile, meaning you can comfortably use an image of any size as the watermark image. The effect doesn't work in Fox Fire. And due to the manner in which we have constructed this site, our exclamation mark is not a true watermark.