Tube passengers will be urged to give up their seats to pregnant women as part of a new initiative.
Research showed 30% of pregnant women were never offered seats
Priority seating signs depicting a pregnant woman, a disabled person and a woman with a child were unveiled by Transport for London (TfL) on Thursday.
TfL said research showed that a third of pregnant women were never offered a seat on the Tube and many wait for five stops before an offer is made.
The signs will be installed on all trains from 10 March.
Mayor Ken Livingstone said: "These signs ask all passengers to give pregnant women the respect to which they are entitled by offering them a seat."
Louise Silverton, deputy general secretary of the Royal College of Midwives, welcomed the move, saying: "The campaign will reduce stress and anxiety levels for pregnant women travelling on public transport."
Recently TfL handed out thousands of badges to expectant mothers to enable commuters to identify them.