A K means Kilo which means 1000. "Kilometer, Kilobyte"
In baseball when a person is struck out, the pitcher will receive a 'K' in the score books. They will also put up the letter 'K' on a sign usually in the outfield.
If you strike out your bank account you have put up a K which means putting 1000 dollars in your account.
Man2: I know but I just struck out the bank account again.
Man: I hear that, another $1000.