I wonder if this is the motorcycle from this article that got posted a few weeks ago.
Heath Ledger almost always moved through L.A. on a yellow Ducati, his head encased in a full-face helmet as he zipped between his home in the hills and his Hancock Park workspace with perfect anonymity. He could put on his mask, hop onto his motorcycle, zoom down Laurel Canyon Boulevard, then leave the bike in front of the Masses' office and sneak inside without a single person catching a glimpse of his face.
http://www.laweekly.com/2008-07-10/film-tv/port-in-the-storm/5