Pop-up balloon on user homepage to notify that there are new notifications

I need to add a pop-up balloon on user home page when there are new notifications (only mentioning that there new notifications and not the detail).
I thought of using this section in header.tpl that shows this pop-ups in:

{if $hasSystemNotifications} ..... {/if}

how can I add a new systemNotification in order to be displayed by this code?
We are on OJS 2.4.6