Inspired by M.C. Escher, 19th Century display type and the Stealth bomber (?), Jonathan Barnbrook and his studio created the newly released Priori Acute, part of Emigre's Priori font family. Initially the letterforms seem peppily, but unexceptionally, rendered in 2d, but then the unsettledness settles in. Each form incorporates multiple perspectives (M. C. Escher, indeed) and it's impossible not to keep staring. I can see why Emigre recommends Priori Acute for "selective situations" as looking at it is akin to that "old lady or young woman" eye trick???definitely not the typeface of choice for road signs.
More here: http://www.emigre.com/EFfeature.php?di=214