Its nofollow. You can check it your self by installing search status add-ons. Then open your G+ profile right click on on search status add-ons - Highlight Nofollow Links. Then it highlights all nofollow links
Google+ used to be do follow (or rather no nofollow as technically "dofollow" doesn't exist). But yeah, it used to be dofollow. Not sure when it went nofollow.
Google Plus link always nofollow because google plus is social networking site and social networking site link no-follow.
Social media sites are set to nofollow, Google+ is not an exception. This is due to the fact that social media sites are link sharing sites. And also to avoid link spamming and link manipulation.
Is google plus links no-follow? I really didn't know before, do all the SNS sites like facebook, twitter links all no- follow?
I don't know no- follow links is good for keywords ranking, like this forum digitalpoint, I check and seems it's no-follow for it's signiture? anyone knows that?