If you're a motorcycle manufacturer, and you have a beloved model name from the past, you might think about filing a trademark application for that name for a few reasons. The two biggest ones are: You plan to bring an updated version of that model to market sometime in the foreseeable future, or else you just want to protect that name against anyone else using it.
I want to say, right up front, that we don't know what the motivation is for Aprilia parent company Piaggio. The only thing we can say with certainty is that Piaggio definitely filed a wordmark application (that's a trademark on a word, or combination of words; often including a logo design but not always) for the name "RSV1000" in the US in January 2025.
While it previously had a wordmark on file for the same name back when the bike was sold in the US, it allowed that older wordmark to lapse over time. This new wordmark only covers the term "RSV1000," and does not involve the word "Mille" at this point in time.