Add icon next to menu

Hi,

Home
Cat 1 -- Cat 1.1 -- Cat 1.2
Cat 2 -- Cat 2.1
Cat 3
Cat 4

If I have my menu set-up like above, with Cat 1.1 being a subcategory of Cat 1, I want to put an image next to the menu item to tell the user that if they hover over this menu item, they will see the subcategories. In my example the image will be down on Cat 1 and Cat 2.

I was thinking the code would be something like this:

<if cat has subcat>
<div menu-sub>
Menu
</div>
<else>
<div menu-nosub
Menu
</div>
</if>

Is this something any one can please help me out with?