Firstly they wouldn't allow that on the tower of London.
Secondly it'd cost too much if they did allow it to warrent it because it'd be completely pointless waste of money as the UK doesn't vote for your presidents and not enough US citizens would see it.
Thirdly it could imply Obama can go into the tower of London as a prisoner and Trump should not. 72% say Obama should be in the tower - see what I mean? Would be rubbish advertising.
