Zebra is going to town on social...
Too many retweets with keywords included around a link
Facebook updates with too many shares from people not in your industry
Any Google+ shares as this will look spammy (Google+ is a graveyard right, so any activity looks suspicious?!)
Owning a Pinterest page - brands only use these for SEO benefit no?
If you've been creating great content which may be being shared extensively by people on the web, some of which might not be bloggers in your niche, then start looking over your shoulder. The Big G doesn't want anyone messing with their rankings.