I think the evidence Ghengis_Jon remembers - ledgers, city tallies,
hoards of tokens, letters, and diaries - all relates to later periods, not the ancient world.
Roman spintria are so
rare, and were also of course not coins, that they are never attested to have been found in groups or
hoards.
The absence of
spintria from
hoards or excavation finds was one of the arguments advanced by a Scandinavian member of Moneta-L for
his ridiculous assertion that
spintria are not ancient but are all 18th-cent.
forgeries!
In the meantime I have heard from CNG's
Peter Lampinen that a
spintria has turned up in an excavation in
Israel.
Anyway, there is practically no ancient evidence at all for possible uses of these tokens.
The
Vienna Museum summary gives a totally false picture of the state of our knowledge.
We do know something about the distribution of free grain in
Rome and the passes that the recipients
had to present. Such a pass is depicted on a
Republican quinarius,
Crawford 473/4, and
Annona is shown holding one on a
rare sest. of Ant. Pius,
BMC pl. 40.1. I believe actual specimens of such passes have survived and are described in Van Berchem's groundbreaking study, Les distributions de ble et d'argent, a copy of which I have at
home. Our tokens on the other hand
had no connection whatever to the grain supply of
Rome.
Similarly there is no evidence at all (beyond the depictions) for the connection of
spintria to prostitutes asserted in the
Vienna summary.
It would certainly be a valid approach, which your BM lecturer seems to have followed, to study the documented uses of tokens etc. in
medieval and modern times, and to speculate on this basis what ancient tokens might have been used for. This would never amount to proof, but might well point you in the right direction.