The best way to promote your brand in emails is to use a customized signature. And WiseStamp is the perfect tool for that.
According to the website,
WiseStamp Email Apps enable users to transform their emails into a powerful self expression and promotional tool. Users can choose in the WiseStamp Gallery from a variety of Email Apps that enable them to easily add dynamic content to each outgoing email such as their latest eBay item, latest Twitter tweet, recent blog post or a cause to promote.
WiseStamp supports all major webmails and is an official Mozilla recommended add-on. Since its launch WiseStamp has reached over 2 million installs and is growing rapidly.
WiseStamp currently works with Gmail, Yahoo, AOL and Hotmail. All you need to do is install it in your browser (Chrome, Firefox or Safari). Then, you are good to go. Start promoting your presence on social networks and/or share your latest Tweet, article, or a random quote to spice things up.
I have used WiseStamp for months and absolutely love it!
Here is what my customized signature looks like in Gmail: