Some tracking codes in the footer of a commercially sent email are easier to decipher than others. It's like geek speak for marketers. With these, and appropriate ecommerce tracking with Google Analytics 360, companies can see how much, if any, revenue is generated by campaigns. It's usually paired with the assumption of "last touch" revenue source, where the last marketing activity a customer takes before a purchase is how credit is applied to a specific inbound or outbound methodology, be it from SEO, email, a product page on a website, a direct mail catalog SKU number, etc.
Here is an example. This comes from the Starbucks Rewards program, and their tracking code is just below the body of the email and above the footer; though many organizations place this tracking code in the AMP Script (if using a Salesforce product) and some place this below the footer/disclaimer text.
I thought that the first two digits were the year of the broadcast, but Starbucks Rewards emails from 2020 also have this 21-15 starter tag. And, it's not sequential to time-order. There are campaigns that ran in January 2020 with the starter tag of 21-14 and emails that were sent in October 2020 with the starter tag of 21-13. So, maybe a campaign type?
The middle "1-0-0" I think a null code placeholder. Here is a tracking example from their "Starbucks for Life" rewards campaign: Ref: 21-13-SFL21-1-0-0-EM-SR-NA-US
The easiest way would be to just ask someone who works for Starbucks marketing. But this is more fun. These tracking codes aren't meant to be memorable; but they are a good way for marketers to attribute sales revenue and customer engagement through email-to-store or email-to-mobile-order sales.
In contrast, retail stores with ecommerce websites often use coupon codes as tracking codes that are static and can be used by anyone whether or not they are a rewards customer; and as such, the coupon code variations reflect a simple code (e.g., holiday20, welcome10).
