Speeding ticket in France

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Sorry no ideas on the ticket

From what I have concluded reading responses here, France is not particularly aggressively in pursuing traffic tickets. And traffic tickets are not part of the immigration data base so I would not worry about a problem when you return. However, Italy is the reverse -- they are very aggressive including debt collectors in the US. Personally I would let it go since you have made the effort to pay it.

Thank you for the timely response!

If the rental car agency gave them your address, they will send you a ticket by mail if they want to pursue it. So just wait and see if it shows up and you can go from there.

I would make every attempt to pay the fine. The National Police more recently have been to know to use collection agencies in the US to collect fine amounts.

Difficult to help without a lot more information, but you should contact the ANTAI and do all you can to settle the fine as quickly as possible:

https://www.antai.gouv.fr/en/

"I would make every attempt to pay the fine. The National Police more recently have been to know to use collection agencies in the US to collect fine amounts."

I would beg to differ, even if U.S. based collection agencies are used neither France nor Italy have legal jurisdiction to collect traffic fines in the United States, they are unenforceable absent an international agreement that would permit this (which I doubt exist). A concern would be though if, upon later return to these countries, there would be any lingering legal ramifications such as being arrested or denial of entry to the country.

It is impossible to get a copy of a fine, and in order to settle this without the relevant piece of paper now that the time to pay online has elapsed, you'd have to know in which French département you were fined and contact the local equivalent of the IRS... In other words: forget about it.
They have your address: if they want to find you, they will.
If this is a standard speeding fine, the "late payment" amount is 375€, plus approx 15% recovery fee if applicable. Being proactive would only save you those 15%.
You do not face any legal consequences; only financial.