Back in 2007-08, coach Doc Rivers shined a spotlight on the blank spot on the wall next to the 1986 championship banner hanging at the practice facility in Waltham. This year? Well, let's just say it's more prominent than a spotlight: (http://www.boston.com/sports/basketball/celtics/extras/celtics_blog/2009/09/the_mysterious.html)So we all know about the 17 banners the Celtics have won, commemorating their 17 NBA championships. But there's a mysterious, blank, 18th banner hanging just next to the 2008 World Champions banner at the Celtics practice facility.Celtics coach Doc Rivers was asked about the enigmatic tapestry."I don't know where it came from," said Rivers. It has an obvious meaning, You can ask the players what it means...Red [Auerbach] did it."I'm all for it. It's as cool as it is promising, since it worked for them two years ago.