If those are icons you use in your interface you might want to rely on an icon theme.
If you’d rather not set all of this up, you can still use an image, with syntax just like those: [[image:AppWithinMinutes.ClassEditSheet@bulletcross.png]] or [[image:AppWithinMinutes.ClassEditSheet@bulletcross.png||style="display:inline-block"]].
Had a second quick question. Not especially familiar with velocity scripts, but would it possible to create a secondary panel that includes the Table of Contents consisting of the headers for the page that the user is currently on? Inserting the TOC directly onto the page with a macro tends to disrupt the layout of bulleted lists, tables, and images, which rely on visual consistency.
It’s possible, you can add macros in Panels 
See Table of Contents in a Right Panel
Have a good day!
Lucas C.