The lower portion of Florida's Turnpike (Miami area) is electronic toll only. I would think that the entrance ramps would be signed "Sunpass/E-Pass/Leeway only" or something like that.
there are big signs at the beginning and end but they don't say what you suggest because the road is NOT electronic toll only. If you use the road and do not have a transponder or other payment system in place, the state sends a monthly bill by electronically reading your tag and getting your address that way. A SMALL service fee is applied.
But what about a rental? Most rental cars today pay a third party to manage the toll collection for their fleet - "or other payment system". When a rental gets a photo taken of the tag the 'system' sees the car as fleet registered and the toll is processed with the bill going to the 'third party' - no fine, they actually get the discount rate. It is the third party that sends a bill to you and any administrative fee - their fee, not the State's. Your rental contract explains this - who reads that? Some rental companies charge A LOT for this service, some charge much less. Some require a decision up front. Some say you choose to participate by "using the system". Some charge only for days used. Some charge for full period of the rental if you opt in. Ya gots to research it.
https://www.sunpass.com/rentalcar