Why do Mormons Wave White Handkerchiefs?

What is the significance of waving a white handkerchief?

When the Mormon Temple in Kansas City is dedicated on May 6th, worthy members of the Church of Jesus Christ of Latter-day Saints, Mormons, will be allowed to attend the dedication ceremony.  There is a point in that sacred ceremony where the white handkerchiefs will be waved in a Hosanna Shout. 
Kendrick Pangman
An educator in both traditional and natural settings for more than a decade, Kendrick Pangman holds a bachelor's degree in history from State University of New York, Albany and a master's degree in education from Le Moyne College. Published in local monthlies around Syracuse, N.Y., Pangman devotes his time to promoting local music and fighting the introduction of hydraulic fracturing in New York.

The shouting of Hosanna in praise of Jesus Christ is written in both the Bible and the Book of Mormon.  The Hosanna Shout was celebrated anciently as part of the Feast of Tabernacles.  Matthew, Mark and John all give an account of a Hosanna Shout given by the throngs of people as Jesus triumphantly rode into Jerusalem.  As Jesus entered Jerusalem his followers cut palms and laid them on the ground before him.  Others waved the palms shouting “Hosanna to the King” as he passed by.  

In the Book of 3rd Nephi, “for the great thing which he had done for them, in preserving them from falling into the hands of their enemies. Yea, they did cry: Hosanna to the Most High God. And they did cry: Blessed be the name of the Lord God Almighty, the Most High God.” Alma 4:32

White handkerchiefs are used as a symbol of purity in praising and honouring the Saviour, Jesus Christ.