' The Sikhs of New York ' organised the " Turban Day " at Times Square on which date?

20 August, the birth anniversary of Rajiv Gandhi, which is celebrated as Sadbhavna Diwas (Harmony Day). Sadbhavana Diwas commemorates the memory of our late erstwhile Prime Minister, Rajiv Gandhi.

Every year on 24th October, United Nations Day is celebrated to commemorate the day of United Nations formation. 

The United Nations is an intergovernmental organization that was tasked to maintain international peace and security, develop friendly relations among nations, achieve international co-operation and be a centre for harmonizing the actions of nations. I was started on 24 October 1945.

In the month/day format 3/14 i.e, Mrach 14th is celebrated as Pie Day as its value is 3.14.

National security refers to security of a nation state, including its citizens, economy&institutions, is regarded as a duty of govt. It is celebrated every year on 4th March. The 1st National Security Day observed in the year 1972.