The RAF Bomber Command War Memorial and the Animals in War Memorial, both in central London, were covered in red paint.
The Metropolitan Police have not yet made any arrests, so the motivation behind the damage remains unclear.
The words written on the memorials have been covered up with plastic sheets after being discovered in the early hours of the morning, but it is believed that "Islam" has been written on each of them.
The Bomber Command Memorial, which was unveiled by the Queen last summer, remembers the sacrifice and bravery of the 55,573 RAF crew who lost their lives in the Second World War.
