I believe it is generally thought that the symbols and monograms represent the responsible issuing authorities. At most mints symbols are the earliest way of identifying issues, then monograms, and finally officials names are spelled out--though there are exceptions to this generalization. The issue in question seems to have come just when the monograms were beginning to replace symbols and did not last to the final phase.
Monograms,
symbols, and dot controls occur simultaneously on these
hemidrachm issues. The three together on a single coin is not infrequent. It is unlikely that all these
symbols represent discrete issuing authorities or connections to individual cities as suggest by Alan. Rather, it is likely that at least one and probably two are secondary controls used for internal accounting and reconciliation in the
mint.
For example if multiple striking teams or anvils were in operation the output of each would need to be identified and reconciled with the initial silver volume allocated to each team. Similarly batches of silver were probably designated to be coined and reconciliation of the total struck
weight with the initial silver
weight would require that coins be allocated to the the correct batch at the final weigh in.
Symbols and even dots/globules/pellets could serve to identify source silver and striking team output in a multi anvil production environment. Many permutations are possible of the accounting and reconciliation need and and how it can be most effectively and efficiently done in the
mint environment.
The key would have been to clearly identify and then match inputs and outputs to ensure that theft and
fraud was minimized in the production process - discrete
symbols and their matching to inputs and outputs are an effective way of doing this.
Sequence the dies, and decipher the sequence of
monograms and
symbols and you can unravel some of the detail of the operation of the
mint. Mind you this is no small task.
