In addition to above, here is another good reference to find Service Tag (Asset Tag), Serial Number etc for IDPA models: [URL] We welcome questions and contributions from all. If you found this useful please give KUDOS to help others find the information also. thanks
A lot of customer find difficulties in finding the service tag for any system as Service Tag details are not often readily provided or available. Dell Service delivery requires the Dell Service Tag in order to facilitate Support, Parts & Dispatch operations. use this guide to retrieve the required Service Tag. Applies to any systems based on Dell PowerEdge server platforms.(a.k.a Mixed IP)  for example DD3300 and DP4400. Link : [URL]  
How to find service tag of a product. (DP4400)