Language, which allows complex ideas to be communicated through symbolic\nsequences, is a characteristic feature of our species and manifested in a\nmultitude of forms. Using large written corpora for many different languages\nand scripts, we show that the occurrence probability distributions of signs at\nthe left and right ends of words have a distinct heterogeneous nature.\nCharacterizing this asymmetry using quantitative inequality measures, viz.\ninformation entropy and the Gini index, we show that the beginning of a word is\nless restrictive in sign usage than the end. This property is not simply\nattributable to the use of common affixes as it is seen even when only word\nroots are considered. We use the existence of this asymmetry to infer the\ndirection of writing in undeciphered inscriptions that agrees with the\narchaeological evidence. Unlike traditional investigations of phonotactic\nconstraints which focus on language-specific patterns, our study reveals a\nproperty valid across languages and writing systems. As both language and\nwriting are unique aspects of our species, this universal signature may reflect\nan innate feature of the human cognitive phenomenon.\n