The Financial Industry Regulatory Authority has ordered U.S. Capital Advisors LLC to pay more than $3.8 million to a group of 19 retirees of Irving-based Exxon Mobil Corp. (NYSE: XOM), Reuters reported. The retirees said Houston-based USCA mismanaged their investments and misled them concerning its trading strategy, according to a securities arbitration ruling. The ruling by a panel of three FINRA arbitrators found USCA liable in the case, along with its brokerage and investment advisory units,…