The organisers behind the blimp however, said they were just "poking fun" and "hope Trump sees it".
Mr Trump's planned visit has been met with plenty of anger, with 50,000 protesters expected to take to the streets of central London on Friday.
Later, Mr and Mrs Trump will attend a black-tie dinner at Blenheim Place - the birthplace of Winston Churchill - in Oxfordshire, hosted by Theresa May.
In June, Defense Secretary Jim Mattis wrote to his British counterpart Gavin Williamson warning that if the United Kingdom wants "to remain the USA partner of choice", it should spend more on defense and noted that France is increasing military spending. "If a balloon flying over London makes people laugh, I think that's absolutely worth it", she says.
Mr Corbyn said that the U.S. president's policies were putting the lives of millions of people at risk.
After a North Atlantic Treaty Organisation summit where he provoked a crisis session to force allies to raise their defence spending, Trump landed in Britain having described the closest USA ally in Europe as being in turmoil over Brexit.
Reunited immigrant children scooped up into parents’ arms
The American Civil Liberties Union, which is arguing the case on behalf of the parents, said that success rate wasn't good enough. Fabian said two of those children have already been reunited, and another 54 will be reunited by Tuesday.
President Trump said the British people "voted to break it up, so I imagine that " s what they " ll do" and "Brexit is Brexit".
In the busy south London neighborhood of Brixton, Victor Greetham, who runs a jazz bar, said he hasn't been to a demonstration since he protested against the Iraq War in 2003, but he planned to attend one of the protests against Trump's visit.
May's government has recently been shaken following at least three resignations of senior members of her cabinet - including Foreign Secretary Boris Johnson and Brexit Minister David Davis, following disagreements on how to exit the EU. But she also warned Trump not to ignore the "malign behaviour" of Moscow when he meets Russian President Vladimir Putin in Helsinki next week.
Britain "is in somewhat turmoil", Trump said before departing Washington, remarking that dealing with Putin might surprisingly be the easiest part of the European trip.
The US president's brash style and hardline "America First" policies have caused consternation across Britain's political spectrum and society.
They are scheduled to spend Thursday night at the US Ambassador's home Winfield House, which is in Regent's Park.