The symbolism of the tonsure at Baptism is that
..... the hair is the first thing which the baby has grown alone
..... so it is sacrificed to God as his or her first fruits
.... it is also a reminder that as life progressses God may ask other and more substantial sacrifices.
This is the symbolism that I know. Is there more? There could well be.
It is the only thing that can be sacrificed from the body without actually draining blood, etc. This symbolism has Samson in mind.
They didn't cut mine, though I have plenty. My son, the same: the cross of his tonsure was quite visible for a while.
Btw, they are supposed to put the cut locks in the baptismal water. Some just give them to the parents which somewhat nullifies the symbolism (unless a reference to the Fifth Commandment).