Self promotion is the key to success in affiliate marketing.
Using your e-mail account's signature line or using a signature line in community forums is a great way to add a bit of advertising to every one of your e-mails or posts. A good tip is that if you are using this medium
to attract visitors to either join an affiliate marketing program or to visit your website where they will potentially purchase something that you're trying to sell, it's a good idea to change your signature line occasionally.
You can rotate advertisements which will help you attract visitors. If you continually have the same advertisement people who see your signature line all the time will become numb to it whereas if you change it regularly, the likelihood of someone clicking on it increases. Change prompts curiousity.