You can just add this cron entry:
Code:
0 12 * * * /usr/bin/yum check-update &>/dev/null ; if [ "$?" == "100" ] ; then CONS=`/bin/ls -l /dev/console | /usr/bin/awk '{print $3}'` ; (/bin/su - $CONS -c '/usr/bin/zenity --info --text="There are new updates available"' &>/dev/null &) ; fi
Once a day at noon (or whenever you set the cron job to run), it will check for new updates. If it finds any, you will get a pop-up message on your screen to let you know. To see the message, manually enter the command:
Code:
zenity --info --text="There are new updates available"
It's not exactly an icon, but it does the job. Personally, I just let my machines apply maintenance daily automatically.