Spotting an empty seat on the tube in London is about as rare as seeing a unicorn galloping down the street blowing glitter through its nose. Wedge yourself onto the carriage of any given tube line at rush hour and you will be lucky to maintain any semblance of personal space, let alone bag an entire unoccupied seat to yourself.
And while this can be annoying on the best of days, it can be a genuine problem for those who have difficulties travelling on public transport due to a disability.
Now, Transport for London (TfL) are taking steps towards making the tube more accessible and comfortable for everyone, with the introduction of a new "please give me a seat" badge scheme aimed at helping those who have a hidden disability.
Thought to be the first scheme of its kind in Europe, TfL hopes the initiative will follow in the success of its "baby on board" scheme, which sees badges given to pregnant women to help make their journeys more comfortable.
The initiative will be rolled out across London on 12 September, with 1,000 people already recruited to start wearing the new blue-and-white badges.
And giving a nod to the scheme, Mayor of London, Sadiq Khan, told BBC News he hoped they would "give confidence" to those who have problems standing on the tube.
In a city where talking to strangers is far from the norm, the badges should be a useful way of communicating if a person needs a seat.
James McNaught, 45, who used the tube to travel to chemotherapy appointments, told the BBC he was "really pleased" with the scheme after deciding to make his own "cancer on board" badges during his treatment. Having radiotherapy on his throat left him unable to talk while the morphine he was on made him appear drunk, so he had no other way of telling fellow passengers that he needed a seat.
"A badge and card could help make a real difference to the lives of people undergoing drug treatment or with longer term conditions or disabilities," he added.