Exactly, 999 is an inverted 666:::

Forthtell: Turn 'em on their head!
http://forthtell.blogspot.com/2011/11/turn-em-on-their-head.html?m=1

TV's Fall Haul: 666 Park Avenue:::

Or something like that — the actual building's address is 999 Park Ave., but when lit from below, the resulting shadow on the building numbers reveal it to be 666, even though that's not how shadows work.
http://m.gawker.com/5947940/tvs-fall-haul-666-park-ave