We worship Siva as Lingam manifested and unmanifested (Vyakta and Avyakta).Likewise for Muruga, the Vel stands for the Form and Formless, The Vel represents only Muruga. Qhatever worship is offered to Vel goes to Muruga.
In Sangam periods a beloved under the pangs of love will become very thin. She will not reveal the truth. Her relatives thinking that she is possessed will exorcise by propitiating Muruga, it is known as 'Veriattu'. At that time they will erect a 'Vel' as a symbol of Muruga. The priest who offciates is called Velan, and he will be wielding a Vel in his hand. He will be possessed by Muruga and he will start foretelling. Thus 'Vel' an instrument become the God Velayuthan. Even now we can see in many places the Vel being worshipped. Devotees prick themselves with Vel as a sort of vow. The pillars near Nandi explsin this. Two sculptures - a Vel is decorated with garlands at the top and the bottom is adorned with a dress. This represents Muruga decked with flowers in his head and attired in his waist.
The credit of spreading Muruga worship in foreign lands goes entirely to the Nagarattars. Wherever they went they built temples for Muruga and established worship.
Lilvanu, the Prime Minister of Singapore was an ardent devotee of Muruga of Tank Road. The Chiness and Malaysians too are worshippers of this Muruga. The temples which at present houses Muruga once had 'Vel' as their deity. That is exactly what these pillar sculptures represent.