I will be traveling to Rome, Italy, unfortunately I could not get a R/T ticket so I purchased two One Way tickets (1 to Rome and 1 back home to the USA). Will this be an issue? And if so what can I show to prove my return to the USA.
No this won’t be an issue. It is possible that the airline will ask you to show your return ticket when you check in for your flight to Rome. This has happened to me when traveling on a one-way ticket. I just pulled up the email with the return ticket purchase confirmation.
I frequently travel on one way tickets due to frequent flier redemptions. Sometimes I am on different airlines each way. No one has ever asked me anything about this when traveling.
Your return ticket is your proof if needed.
Same experience as Carol. Frequently we don't even have a return ticket but in nearly 50 years of travel to Europe we have never been ask about return plans. I supposed if you look like your are going to over stay your visa, I guess they could ask the question. (Have no idea what that look would look like.) I know of no regulation that says you need a return ticket.
At the most, it's a question that might be asked, for which you have an answer. Screeners often ask questions just to see if you react suspiciously.