President Pratibha Patil has unveiled two unique and innovative stamps, including a special Khadi Stamp on Mahatma Gandhi, to mark the beginning of a week-long 6th World Philatelic Exhibition in New Delhi.Inaugurating the exhibition, styled as INDIPEX-2011, Patil underlined the need for spreading Mahatma Gandhi's message of non-violence across the world. She said the Khadi stamp was being issued on Mahatma Gandhi, the apostle of non-violence as it is connected with Indian sentiments linking to its freedom movement.The President said the Father of the Nation had chosen Khadi as a symbol of the unity of India against the colonial power, and its use portrayed the self-reliance and dignity of the Indian people.The exhibition will showcase some of the finest and ratest stamp collections from around the world reflecting the history, culture, socio-economic behaviour, sports, environment across countries and people.Speaking on the occasion, minister for communications Kapil Sibal said the Centre had launched a campaign to encourage philatelic activities among younger generation.AIR correspondent reports that the other highlight of the exhibition is My Stamp, in which one can get his own image as postal stamp. It is also known as personalised stamp. The exhibition also marks the centenary of the world's first airmail flight, which took place in India between Allahabad and Naini on 18th of February in 1911.