The longest word in the English language is the chemical name for titin with an mind-boggling 189,819 letters. If you want read it, check it out here. According to the Minecraft Wiki, there are four rows on a sign which can each fit fifteen letters. 4x15 is 60, so that's 60 letters and/or characters per sign. 189,819 / 60 = 3163.65. (and no, I did not do it on paper) That means it takes 3163.65 signs to write out the longest English word.