Seems Google is testing or launched a new feature to help business owners reclaim and login to their Google My Business listing. Elizabeth Linder posted a screen shot on Twitter of this feature that has the option for you to click on a button to "Own this business? Claim it now."
Krystal Taing explained "For anyone beginning to see this on your listings, it is a new #GMB feature. It does not mean your listing is unclaimed but is intended as an easier path to begin the claiming process for users that may have mislocated their account info."
Joy Hawkins added in the Local Search Forums "this change is slightly different. Now it shows up even if the listing is already claimed by someone else. It's caused a bit of confusion. I just realized though that you can see if a listing is verified or not by using an Incognito tab. If the "Own this business" shows up while you're logged out, it means the listing is unverified."
So now all claimed listings can show this when you are signed in. This can be a bit annoying and maybe confusing?
Forum discussion at Twitter and Local Search Forums.