By Ilaria Grasso Macola The Financial Conduct Authority (FCA) has slapped City stock broker Sigma with a £531,000 fine after it failed to identify 97 suspicious transactions. The watchdog also found the firm guilty of inadequately reporting 56,000 contracts for difference – an insurance tool used by market participants – between December 2014 and August 2016. Both former and current managers have also been fined, as the FCA believed Sigma’s failures stemmed from the board’s inadequate governance. Former chief executive and director Simon Tyson was fined £67,900, while ex-director Stephen Tomli…