A service information board in London Bridge Tube station showed a message of solidarity after the London Bridge terrorist attack, that claimed the lives of Jack Merritt and Saskia Jones.
The murders committed by convicted terrorist, Usman Khan, have raised questions over the early release of certain prisoners and the efficacy of rehabilitation programmes.
Sadiq Khan called on Londoners to come together "in a spirit of defiance" against terrorism during a vigil for the victims of Friday night's attack.
The London Mayor was joined by Prime Minister Boris Johnson and Labour leader Jeremy Corbyn at the memorial to Jack Merritt and Saskia Jones in Guildhall Yard in the City of London on Monday morning.
Also present were Metropolitan Police Commissioner Cressida Dick, Home Secretary Priti Patel and Liberal Democrat candidate Chuka Umunna.
After a minute's silence at 11am, Mr Khan said: "We come together this morning as Londoners to remember, to honour and to mourn the innocent lives lost as a result of this horrific terrorist attack on Friday.
"The best way to defeat this hatred is not by turning on one another but by focusing on the values that bind us."
The mayor thanked the public and members of the emergency services who "ran towards danger, risking their lives to help others they didn't even know".
Mr Khan called on Londoners to "draw inspiration from the lives of Jack and Saskia who, from a very early age, chose to dedicate themselves to helping others".
He added: "We come together in condolence but also in a spirit of defiance to say that London will never be cowed or intimidated by terrorism."