Rosa Parks (pictured here in 1955; that's Dr. Martin Luther King, Jr. in the background).
According to Wikipedia, California officially commemorates Rosa Parks Day on February 4. (Ohio also has a Rosa Parks Day, but it is observed on December 1, the anniversary of the day Ms. Parks was arrested on the bus in Montgomery.)
Monday, February 4 is also World Cancer Day, a day, according to the linked website, "to raise our collective voices in the name of improving general knowledge around cancer and dismissing misconceptions about the disease."
Some of the Usual Suspects (Punchbowl Holidays, for one, but also Days of the Year) proclaim Monday to be Thank a Mailman Day. However, Usual Suspect Gone-ta-pott.com insists that Thank a Mailman Day should be observed on February 5. We'll let you decide when (or whether) to thank your friendly neighborhood letter carrier. The choice between days is probably insignificant; according to Wikipedia, "The United States Post Office (USPO) was created in Philadelphia under Benjamin Franklin on Wednesday, July 26, 1775, by decree of the Second Continental Congress." And that's neither Monday nor Tuesday.