What is the significance of the red knot in the wedding ceremony?

It is not like this in the wedding ceremony. Are you talking about Chinese wedding in old time? At that time, there was also a red square silk on the bride's head. A red ribbon with a knot was in her hand. The groom pick the other end of the ribon and lead the way of the bride to the wedding. After the ceremony, they became the husband and wife, then the bride could raise the silk scarf on bride's head and know what does she look like.