The System Identification Number was introduced in the First Edition rulebook ("Glossary of Slang in 2050," SR1, p.161). It was coded into the average citizen's credstick (SR1, p.125), back before there were commlinks.
Rules for forging credsticks and IDs first appeared in SR2, Neo-Anarchist's Guide to Real Life (p.103).
The Third Edition rulebook gave the subject more attention ("SINless," SR3, p.238).