idiograph
/ˈɪdɪə(ʊ)ɡrɑːf/ /ˈɪdɪə(ʊ)ɡraf/noun
A piece or sample of a person's own handwriting; an autograph.
Origin
Early 17th century; earliest use found in Henry Cockeram (fl. 1623–1658), lexicographer. From idio- + -graph; compare Byzantine Greek ἰδιόγραϕον autograph.