Hi Charles,
There is help pop-up on message body field that lists all available substitutions. Just copy paste from there:
"In a badge message, certain variables can be inserted into the subject and/or body of a message so that they will be replaced with real values when the message is sent. The variables should be inserted into the text exactly as they are shown below. The following variables can be used:
%badgename%
This will be replaced by the badge's full name.
%username%
This will be replaced by the recipient's full name.
%badgelink%
This will be replaced by the public URL with information about the issued badge."
Hope this helps!
Yuliya