A signature is a handwritten depiction of someone's name, nickname, or even a simple "X" or other mark that a person writes on documents as a proof of identity and intent. The writer of a signature is a signatory or signer. Similar to a handwritten signature, a signature work describes the work as readily identifying its creator. A signature may be confused with an autograph, which is chiefly an artistic signature. This can lead to confusion when people have both an autograph and signature and as such some people in the public eye keep their signatures private whilst fully publishing their autograph.

Handwriting is the writing done with a writing instrument, such as a pen or pencil, in the hand. Handwriting includes both block and cursive styles and is separate from formal calligraphy or typeface. Because each person's handwriting is unique and different, it can be used to verify a document's writer. The deterioration of a person's handwriting is also a symptom or result of several different diseases. The inability to produce clear and coherent handwriting is also known as dysgraphia.