We need three files for this:

• signature.txt: you should point your mail client to this one
• signature.tpl: here is the common text to display, something like “xmms is now playing:“
• signature.sh: the script first copies the contents of the template file to the final signature file, and then adds the current song as a new line.

Download signature.sh:

#!/bin/sh
cat /home/etd/scripts/signature.tpl > /home/etd/scripts/signature.txt
echo $1 >> /home/etd/scripts/signature.txt

you only need to call the script using the change song xmms builtin plugin.