updated 03/20/2013 AT 11:00 AM ET
•originally published 03/20/2013 AT 9:20 AM ET
The Duchess of Cambridge received an appropriate memento of her trip to a London tube station Wednesday – a “Baby on board!” button.
“I’ll make sure I wear this at home,” Kate, laughing, said as she was handed the badge, emblazoned with the London Underground logo.
Wearing a Malene Birger coat and black beret, Kate was along for the ride with Queen Elizabeth and her husband Prince Philip. The visit helped mark the 150th anniversary celebrations of the subway network.
Touring the Baker Street station, Kate, 31, revealed she “missed” traveling on the public transport system.
“She said she used the tube on a regular basis before she was married,” Howard Collins, chief operating officer of London Underground, tells PEOPLE.