During the Renaissance, Spanish sculptors would often carve their statues out an expensive form of marble; if they made a mistake they would patch the marble with cera(wax). However in the rare event of a flawless statue that required no patching the statue would be hailed and celebrated as a "sculpture sin cera" or a "sculpture without wax." The phrase was evntually derived as anything honest or true. The English word "sincere" is derived from the Spanish "sin cera"-"Without Wax." So when i say something is Without Wax or I sign a letter as such; I am merely saying "Sincerely."

Without Wax, Corey

--source- Digital Fortress, by Dan Brown