Coinage, the practice of minting small bits of metal with distinctive marks, appearing in the second half of the 7th century BCE, had a transformative impact upon ancient economies and societies. Controversies endure concerning the original function of ancient coinage, in particular the respective role of states and markets in its emergence. Applying information-theoretic measures to a corpus of 6859 distinct coin types from the Ancient Mediterranean world, dated between c. 625 and c. 31 BCE, we show that the symbols minted on coins (designs combining images of plants, deities, animals, etc.) became increasingly informative about a coin’s value. This trend was specific to value-relevant information, as distinct from information concerning issuing states. Coin designs also carried more information about higher denominations than about lower ones. Before numerical or written marks of value became widely used on coinage, these iconic symbols were carrying economic information.