Nearly all movie trailers shown in theaters, and on the web, come with a so-called green tag, saying they are approved for all audiences, or a red tag, saying they are approved for only restricted audiences. Since 2000, many theaters will not run red tag trailers; Warner Brothers will not make red tag trailers, and Universal Pictures has not ran one in theaters since "American Pie" in 1999. Wishing to show audiences more "edgy" previews, the producers are looking to the internet.

Rob Zombie’s “Halloween” remake became the first to display a new yellow tag, signaling that the movie was rated PG-13 or above, and the preview was “approved only for age-appropriate Internet users” — mandatd by the MPAA as visitors to sites either frequented mainly by grown-ups (as determined by Nielsen's Web Demographic reports) or accessible only between 9 p.m. and 4 a.m.

This August’s “Superbad” (autoplay music...) has an R-rated, red tag internet trailer, which MPAA regulations require a viewer to pass an age-verification test, in which the viewer 17 and older has to match their name, birthday and ZIP code against public government records on file." [via nytimes.com]
posted on Jun 24, 2007 - View this thread

Remember that Shining trailer from a few weeks back? Now they've done it with Big. (embedded WMV)
posted on Dec 1, 2005 - View this thread

Shrek 2: The First Five Minutes. Forget trailers; this is the future.
posted on May 22, 2004 - View this thread

"Version 1 is always the most elegant, most evocative trailer that is ever created -- and the one that is never released." The New York Times has an interesting look at the process of making movie trailers, with Signs as an example (minor spoilers).
posted on Aug 5, 2002 - View this thread

Lord of the Rings Trailer released...wow is it something. I wasn't too sure about this one before (Liv Tyler as Arwen? Oy...), and, while the acting may suck, it looks like it's going to be quite a spectacle.
posted on Apr 7, 2000 - View this thread