Is HSBC's $1.9bn (£1.2bn) fine enormous or a drop in the ocean?

Well, it's a record for the offence of money laundering and breaking sanctions, which could be said to underline the gravity of the bank's actions. On the other hand, the sum represents about four weeks' earnings given the bank's pre-tax profits of $21.9bn last year.

The financial pain is easily bearable. Indeed, the steady upward progress of HSBC's share price since the scandal exploded in July was unaffected on Tuesday morning.

Shareholders like the idea the affair is settled and they trust that chief executive Stuart Gulliver's new-broom regime won't fall foul of the US department of justice's new independent monitor,k who will assess how the bank implements its pledges to do better.

Gulliver even has a glowing testimonial to wave as HSBC starts its probation period. "Management had made significant strides in improving 'tone from the top' and ensuring a culture of compliance permeates the institution," said the DoJ.

But HSBC investors may also like something else. The New York Times reports that some DoJ officials wanted to bring criminal charges against the bank but eventually decided not to for fear such a move would put the future of one of the world's largest banks at risk and thus threaten global financial stability.

We don't know the weight of that tale and maybe the fear of financial chaos was exaggerated. But the idea that a bank could be "too big to prosecute" is alarming. It sends a message that, whatever the scale of wrong-doing, the world's biggest banks can never lose their licence to operate overnight. Instead, a hefty fine can always make the problem go away.

Is that really a sensible message for regulators to send? Is their hand really so weak? On this occasion, HSBC's words of contrition and promises to behave properly sound sincere. But will that always be the case for all big banks everywhere and forever?

The DoJ should clear up this sub-plot speedily. If money laundering on the scale admitted by HSBC doesn't provoke a prosecution, what would?

Al Jazeera speaks to Bill Black about HSBC

Al Jazeera's Tony Harris spoke live to Bill Black, economist and former US federal regulator, on HSBC and Standard Chartered banks being hit with heavy fines.