Definition of "sig"

Your sig should ideally be four or five lines long, six or seven at the maximum. Since it will be repeated on hundreds of messages, a long signature wastes bandwidth and is therefore rude.

1995, Vince Emery, How to grow your business on the Internet

Posting good content is the best way to get people clicking your sig link.

2004, Brad Hill, Building Your Business with Google For Dummies, page 48