So I just got my camera back from Sony for the vignette issue (they almost fixed it - I think I'll live with it) and there's a new sticker - silver with red letters under the viewfinder, near the hinge, that says "Warranty Void if Removed"

It was hastily applied and sticks out the side and looks bad, and will probably get pulled off soon from normal usage.

Of course I want to remove it, but it will void my warranty, I think.

Anyone have any ideas what this is covering up, and why they felt the need to apply it to my camera after the fact?

Give them a call and ask, Eric. It likely hasn't anything to say at all.