As far as I know, the way cron determines the subject is hardcoded in the cron source code. Anyway, you can force the cron job to send a custom e-mail instead of the default one, redirecting the standard error to the standard output and piping the result of the job to the mail command using a custom subject. For example:
Code:
0 6 * * * /home/user/nameofscript.sh 2>&1 | mail -s "nameofscript.sh has failed" user
