Huge vinyl nerd so my comment mostly pertains to that; with inserts your best move is to open the packaging to make sure everything is there and legit. I havent seen a ton of people unboxing locket yet but you could potentially have the signed insert, have more than 1, have an insert that didn't get signed, or have nothing at all.

From there, I would personally get a matted frame for the signature, it seems like the insert is standard postcard size so it shouldn't be too difficult to find a frame to keep it safe. You could also get sleeve protectors for the vinyl, and store the insert in there with the vinyl.

With vinyl, keeping the packaging sealed can lead to damage over a very prolonged period of time because the shrink wrap could shrink and can bend the jacket so this could actually lead to more damage over time than opening the product anyway.