Most US-issued cards are online-PIN.

In Europe, many of our cards still are off-line PIN, as in the PIN is embedded into the chip on the card and thus, does not require contacting the card issuer. A PIN entry is required for every transation that has a card insert ; sans contact <50€ transactions are approved without PIN generally.

In France, the vast majority of machines thesedays will accept online-PIN from MC and Visa worldwide (Amex is far less accepted in Europe). Thus US cards will not be an issue at most public transit kiosks, toll booths, etc... at stores you will be given a paper slip to sign. Or maybe not, sometimes the cashier just doesn't care because signature is not the usual way to authenticate.

Where problems may occur : older automated fuel pumps that still only use off-line PIN. These are scattered and generally the exception; the ones at the autoroute rest stops will be newer.

I think only France has widespread automated fuel pumps though. In Italy, Espagne, Germany, Suisse, most places you fill the car/moto first and then go inside to pay.