In this paper I argue that the Stoic theory of signs as reported by Sextus Empiricus in AM and in PH belongs to Stoic logicians which precede Chrysippus. I further argue that the PH-version of this theory presupposes the version in AM and is an attempt to improve the older theory. I tentatively attribute the PH-version to Cleanthes and the AM-version to Zeno. I finally argue that the origin of this Stoic theory is to be found in the Dialectical school (...) (probably Philo of Megara) whose theory of signs has been preserved in Pseudo-Galen, Historia philosopha cap. 9. (shrink)