ZTL Warning App

No app can be as updated as the signs, but Waze warns about all cameras including those of the ZTL areas. Or, At least, the Waze community tries to point out every camera.

There is also an unofficial site: https://www.accessibilitacentristorici.it/ztl?lang=en mapping all ZTLs by Region and City.

There is something even better than app, if you look at the side of the road there are signs telling you about all kind of things, including ZTLs. https://en.wikipedia.org/wiki/Road_signs_in_Italy

In Sicily, I found the ZTLs to be well marked. As Badger noted, if you know what they look like they are normally easy to spot.

Using common sense and reading signage is your best bet.

When we traveled all around Tuscany, we had no problems identifying and avoiding ZTLs. We didn't drive in Florence. We took the bus in from Greve. It cost less to ride the bus than it would have cost to park. We followed the rule of thumb that anywhere within the walls of a hill town like San Gimignano, Volterra, Radda, etc. is ZTL. We did visit Siena, and found the ZTL area was well marked. We parked at the soccer field adjacent and walked into the historic area. ZTLs are only in towns, you don't have to worry about country roads. However, you do need to strictly observe posted speed limits, since the use speed cameras both in and out of towns.

I suggest you buy a good map of Italy before traveling. Also, get a good map of any large cities like Rome and Florence as well. Go online and look up the towns you are planning to visit. Usually there will be a map that shows parking an ZTL.