It's the red square with a starburst in it which appears next to new posts, unread forums, etc. If you use the "mark forum read" link, you'll note that the LRPD disappears next to the forum, and posts are similarly unflagged. When a new post appears, so does the LRPD. This is Scott's evil plan at world domination, as swatting LRPDs rapidly becomes a game of whack-a-mole.
\r\n\r\nThe term also applies to the quotes which appear at the bottom of pages, also called "lepardisms".