This article is about the conception of truth and signification in Augustine's early philosophical writings. In the first, semantic-linguistic part, the gradual shift of Augustine's position towards the Academics is treated closely. It reveals that Augustine develops a notion of sign which, by integrating elements of Stoic epistemology, is suited to function as a transmitter of true knowledge through linguistic expressions. In the second part, both the ontological structure of signified (sensible) things and Augustine's solution to the apparent tautologies of mathematical truths are examined. Again his notion of sign turns out to be the keystone; this time, however, the natural in contrast to the conventional sign of linguistic expressions. In their complementarity, both parts show how Augustine intensely struggles with and (partially) overcomes the skepticism of the sensible world through his conception of sign and signification.