I actually like this suggestion, because now that a normal robbery on players doesn't give as much cash as before so you will have a chance to rob their bank for more cash.
Mike wrote:
I think actually making someone guess a PIN would be pretty difficult. There's 10,000 possible combinations...
Some similar idea might work though. Perhaps when you rob someone on-foot as usual you have the chance to steal their ATM card and then you can try and guess their PIN (scripted, like a 1 in 10 chance or something).
Also, should probably make it that the player drops the card if he dies after robbing somebody before using the card at bank.