I've found that in some environments version numbers are stripped from jar files making it difficult to determine the version of ActiveMQ someone is running. So I created a little Version class that reads properties from a file that is created by the build process. Then you just execute the main method in the Version class to get the following project output:
Project Version: 5.2-SNAPSHOT
Build Timestamp: 2008.08.20 11:39:47 MDT
Java Vendor: Apple Inc.
Java Version: 1.5.0_13-119
OS Architecture: i386
OS Name: Mac OS X
OS Version: 10.5.4
The only thing missing is the SVN revision number. That's more difficult to add.