It’s May, which means “proxy season” in the corporate world. This is the time of year when publicly traded companies hold their shareholder meetings, and investors can vote on resolutions to change corporate policies. The votes can have plenty of clout because huge private investment firms such as BlackRock and Vanguard weigh in, as do major public shareholders such as California’s and New York’s employee retirement funds with billions of dollars in stock under their control. When they want something, CEOs listen.