Why May 12th? As you can see from the information on womeninmaths.org it is the birthday of Maryam Mirzakhani; from the excellent St Andrews University MacTutor site we can read a biography of Maryam Mirzakhani.
Check the Twitter posts on this day, #May12WIM.
This site, Women in Maths was created by a student member of The Institute of Mathematics and its Applications (IMA).
Exploring this page on womeninmaths.org, note the video Journeys of Women in Mathematics a film created by the IMU Committee for Women in Mathematics.
It seems appropriate to link to my post Women in Mathematics written earlier this year to celebrate International Women’s Day.