Wikipedia
Asses signata ( Latin, "stamped bronze", singular aes signatum) consisted of cast lumps of bronze of measured quality and weight, embossed with a government stamp, used as currency in Rome and central Italy before the introduction of the aes grave in the mid 4th century BC. When exactly they were first made is uncertain. Popular tradition ascribes them to Servius Tullius, but due to the high quality of art found on even the earliest specimens, this seems very unlikely. A date in the midst of the 5th century BC is generally agreed on. Designs featured are that of a bull, an eagle, and other religious symbols.
The earliest asses signata were not cast in Rome proper, but in central Italy, Etruria, Umbria, and Reggio Emilia. They bore the image of a branch with side branches radiating from it, and were called Ramos Seccos ("dry branches" in Italian). They did not equate to a set weight standard, varying from about 600 to 2500 grams when complete. They were usually broken into subdivisions, and there are very few complete specimens surviving today. The surviving ramo secco bars are usually quarter, half or three quarter bars, or minor smaller pieces which could be classified as asses rudes. The same fragmentation into smaller change applies to later asses signata issued by the city of Rome, which did correspond to the Roman heavy standard for the as. They weighed approximately 5 as when whole. They could technically be termed a quincussis, although they are not marked with any value.
The Roman aes signatum conforms more strictly to size and weight standards because they are an official issue, where the ramo secco bars were more of a recognizable item of barter exchange that would be weighed, rather than taken at a face value. Ramos seccos were not issued by governing bodies, and could have been made at any foundry facility.