http://schema.org/True
http://schema.org/False

"One thing, though: In the current version of schema.org, False and True are subtypes of Boolean. They should be instances / enumerated values."

Mostly recently pointed out by Martin Hepp, http://lists.w3.org/Archives/Public/public-vocabs/2014Sep/0191.html

(There's also the issue that such values very often show up as literals in data, even if they should be URIs. Could either try to fix documentation to encourage URI use, or document this as an 'expect the unexpected' pattern.)