That's a bit naive I think. First it wouldn't be very effective, banks are banks, that is their expertise, just because there's a reward doesn't turn bankers into policeman that will detect and act on money laundering. Then, who shall pay for the reward. The government, the central bank? Tax reductions? How valuable is a cash reward for one of the big banks anyway.
Then on top of that politics come into play, with all these increasing trade embargoes and bi-lateral agreements, many transactions could be interpreted either as laundering or legit, depending on interests.
