Today is the Feast Day of St. Agnes, Virgin and Martyr, whose name closely resembled Agnus or Lamb in Latin. Her martyrdom also represents the similar Sacrifice of our Lord, the Lamb of God on the cross. This is why this day is the day selected for the blessing of a special lamb-wool sewn shoulder-band like vestment, called the pallium, by the Pope.

http://en.wikipedia.org/wiki/Pallium

What is a pallium? It is a woolen cloth, shaped like two connected Y-alphabets worn around the shoulders, and only worn by bishops possessing Metropolitan character (Metropolitan Archbishops), that is the authority over other bishops as overseers of particular Provinces of the Church, as the pallium signify this authority that has been given to them, and also represents the link that they have to the Bishop of Rome, Vicar of Christ, the Pope.

The pallium itself can also represent the sheep being carried by the shepherd, which represents us, the faithful, the sheep, being entrusted in the care of the Metropolitan Archbishop, who is the shepherd.

For those of us in Singapore in particular, and other Archdioceses directly subject to the Holy See (not part of any Provinces of the Church), our Archbishops do not wear this pallium, and the reason was noted above, as they do not oversee any other bishops in a Province of the Church. This is why, Singapore’s Archbishop, Nicholas Chia, do not wear a pallium, while the Archbishop of my hometown, Palembang, wears one, as he is the Metropolitan Archbishop of the Church (Ecclesiastical) Province of Palembang, overseeing the two Dioceses of Pangkalpinang and Tanjungkarang in the region.