What is a Signature?
Internet Marketing Dictionary | Signature Files

A signature is a block of text, often including a link, that you add to the end of your email messages, to forum posts and to blog comments.

Internet marketers use signatures or signature files in a number of ways to boost web traffic.

Email signatures

A well written email signature will get the attention of the reader. It should also include one or a few links to web pages. In most email software like Outlook, such links will be active in the sense that when they are clicked the reader is taken to the underlying web page.

Forum signatures

Forum signatures are similar to email signatures but they appear in posts you make to forum. Again, writing good copy will attract attention and clicks. But there is a second issue with signatures that appear online: are the links enclosed by NoFollow tags?

NoFollow tags essentially tell the search engines not to follow the links for the purposes of ranking the site they link to. This counteracts a process called comment spamming.

Before NoFollow tags were developed, marketers used to write comments on as many forums as they could knowing that each one could be used to generate a link back to their sites. This in turn would boost their rankings in the search engines.

NoFollow tags put a stop to that.

Blog comment signatures

Blog comment signatures are very similar to forum signatures and before the advent of the No Follow tag, would often be used by marketers to boost page ranks.

Whilst there are still many forums and blogs where comments are allowed and No Follow tags are not used, most marketers find in practice that a more productive and ultimately more profitable way to use signatures is by providing valuable content whilst making sure that their web address is visible.  Note that most blogs and forums that allow postings usually let you include an active link in your signature. This link will work if clicked even if it is tagged with the NoFollow attribute.