Upvote:2
Ostia was a Roman port, possibly the first of their colonies. As such, the script should have been based on the Latin alphabet, which itself appears to have been derived from the Etruscan script.
Looking at graffiti found in the ruins there was a fair amount of variability in writing of Latin characters.
Upvote:3
There is no such thing as "Ostian script". Ostia is known for having been the source of a relatively large number of well-preserved Latin inscriptions (one is shown below). These inscriptions show the same variety of different Latin letters found at Rome itself and in other places within the Roman Empire. Latin inscriptions vary, as one might expect, because each stone cutter had their own style