Rongorongo is a system of glyphs discovered in the 19th century on Easter Island (a.k.a. Rapa Nui) that appears to be writing or proto-writing. More than 20 examples of the script, engraved onto hardwood plates and other objects, have so far been discovered. The forms of the glyphs are standardized contours of living organisms and geometric designs about 1cm high.
Wikipedia has an entire article documenting the various attempts which have been made at deciphering the texts - none of which has so far been successful.