Some users like to add small image thumbnails to their tootips to hint what is to be found there. This is an easy process as the tooltips accept html:
You'll need to link to the image however, so if you upload it to your media library, you'll need the image's url to properly display it. The code you place in the tooltip will look just like this:
<img src="http://www.mapifypro.com/images/tunnel-t.png" align="left" alt="tunnel" height="75" width="75" style="padding-right: 15px;">
You'll replace the url with that of your desired image, and adjust the other settings accordingly. The padding adds a bit of breathing room, and the align left makes sure the text appears to the right of the image, instead of below it.