Transport for London's (TfL) first purple roundels have been installed at Elizabeth line stations for the first time.
The latest version of the historic design has appeared at stations including Tottenham Court Road, Farringdon and Custom House.
Designers attempted to ensure it is distinctive from the existing London Underground and London Overground symbols.
The roundel, originally known as the bar and circle, was first used as a platform name board at the station now called St James's Park, in 1908.
The new £14.8 billion east to west railway is known as Crossrail during the construction phase but will become the Elizabeth line once services begin later this year.
London's deputy mayor for transport, Val Shawcross, said: "The Elizabeth line will truly transform travel across London and the South East.
"The installation of the roundels incorporating TfL's iconic design shows how close we are now to the line opening, with new stations right at the heart of central London."
Services will begin on three routes from December: Paddington to Abbey Wood, Paddington to Heathrow and Liverpool Street to Shenfield.
The line will fully open in December 2019, with trains running from Reading and Heathrow in the west through 13 miles of new tunnels to Shenfield and Abbey Wood in the east.
London's transport commissioner, Mike Brown, said: "No other city is as defined by its transport system as London.
"The roundel is at the heart of our heritage, guiding Londoners and visitors to our city for over 100 years.
"Our state-of-the-art new railway, the Elizabeth line, will balance cutting edge engineering with the familiarity of traditional TfL design."
The Elizabeth line will increase central London's rail capacity by 10%, with a train every two and a half minutes at peak times.
The new trains will be 200 metres long (650ft) - almost twice the length of a London Underground train - and able to transport up to 1,500 passengers.