From marks to names
Before widespread literacy, many people authenticated documents with a simple mark, a seal, or an X rather than a written name. As handwriting instruction spread, a person's written name itself became the mark of identity, tied to their own hand rather than a shared symbol or stamp.
Why signatures became stylized
As signing became a routine part of business and legal life, individual handwriting styles diverged further from careful penmanship into faster, more personal, and harder-to-copy shapes. A quicker, more idiosyncratic signature was, in practice, more distinctly your own than a slow, legible one.
Digital signatures today
Modern signature tools try to recreate that same sense of a personal, non-uniform mark, whether through drawing input or, in SigVela's case, a stroke-based engine that varies each generated signature rather than stamping the same font shape every time.