Earlier quoted context omitted.
How is it money laundering when the money is already in the bank and thus accounted for?
Mob boss has lots of money and needs to launder it. Mob boss starts a building company, paying the employees with dirty cash (but hey, no income tax, so no ones complains). Building company charges customers, but asks for it in cash. Dirty money goes out to construction employees, clean cash comes in from customers. The Bank flag is just saying there is laundering occurring near the money.
Laundering money is almost always done through b2c businesses where it's harder to trace all the customers. You start a cafe, and then you say you had 1.000 customers daily when you really had 100. You pay the tax for the remaining 900 coffees and now your money are clean.