Signature:
It is a 1D functional representation of a boundary & may be generated in various ways.
One of the simplest is to plot the distance from the centroid to the boundary as a function of angle.
Signatures generated by this method are invariant to translation but they depend on rotation and scaling.
Normalization with respect to rotation can be achieved by finding a way to select the same starting point to generate the signature, regardless of shape’s orientation.