These are defined in Unicode 6.2 at http://www.unicode.org/charts/PDF/U25A0.pdf

Personally I'm looking to add support for the ▾ (U+25B8) and ▸ (U+25BE) symbols for use with the Vim NERDTree plugin, but it would make sense to add the entire geometric shapes set at the same time.