Hexadecimal (or equivalents, 770AD-1900s) (references)

44 41 4F

Leonardo da Vinci (1452-1519; backwards) (references)

American Sign Language (origins from 1620-1817 in Italy and, especially, France) (references)

Semaphore (1791, in France) (references)

Braille (1829, in France) (references)

Morse Code (1836) (references)

-..    .-    ---

Dancing Men (Sir Arthur Conan Doyle, 1903) (references)

Binary Code (1918-1938, probably earlier) (references)

01000100 01000001 01001111

HTML Code (1990) (references)

&#68 &#65 &#79

ISO 10646 (1991-1993) (references)

0044 0041 004F

British Sign Language (Fingerspelling, BSL; 1992, British Deaf Association Dictionary of British Sign Language) (references)

Encryption (beginner's substitution cypher): (references)

383549