a transparent lens cap for video cameras and SLRs that says "take off the lens cap."
Obviously, an OEM item, not an aftermarket thing. Other than tradition, is there any reason they're black?
While we're at it, have you ever noticed how often people leave the stickers on their digital cameras? The ones that brag about resolution and stuff... The stickers first got on them because even though only one out of a 100 cameras are opened in the store and put on display, it was worth prettying up every camera with a display sticker just in case.
But now, the sticker lives on, marketing the camera to every person who sees it. I had my picture taken by a Sony camera the other day and the logo was so big I can still picture it.