You can now add up to 10 tags to any of your Auto Scaling Groups. You can also, if you'd like, propagate the tags to the EC2 instances launched from your groups.
Adding tags to your Auto Scaling groups will make it easier for you to identify and distinguish them.
Each tag has a name, a value, and an optional propagation flag. If the flag is set, then the corresponding tag will be applied to EC2 instances launched from the group. You can use this feature to label or distinguish instances created by distinct Auto Scaling groups. You might be using multiple groups to support multiple scalable applications, or multiple scalable tiers or components of a single application. Either, way the tags can help you to keep your instances straight.
Read more in the newest version of the Auto Scaling Developer Guide.