I'm talking about having the +1 button on pages of your website - e.g. product pages (info here). If there have been a number of people +1 a particular product then that may help the position of that page organically - I think even if you aren't signed in.
You wouldn't +1 at the SERP stage if you haven't been on the site but your friends might have done which could input into it.
All guesses though