How does the government track money laundering?

Question

In the movies, they're always mentioning things like these are marked bills. Marked with what? I asked my dad and he said something about the serial numbers, but didn't really explain. Can someone explain the process?

Answer 1

Say if you have a huge sum of money  British Pounds in cash . You take it to the hundreds of travel agencies around Ethnic  London particularly and tell them who you want to send it to and where. ... They find the person in the other country and pay them in their local currency and you hand over the agreed sum in British Pounds here. Done ===All completed over the Mobile Phones =====No transaction paper trails are not  created. There are a number of alternatives . Millions of British Pounds leave Britain every month . Lucrative Scams . Open Secret ,but our Government prefers to turn a blind eye.

Answer 2

There are serial numbers on every bill. Police forces develop strategies in which the marked bills get into the hands of criminal which are likely to launder the money. The marked bills become evidence.

That is tracking money, but generally they already know where it is going in the sense of tracking it.

Answer 3

I think it does have something to do with the serial numbers on the money that is how they track it