Funky little box in comment editor

What is this little box thing that shows up in the edit comment box when I add a comment at confluence.atlassian.com? It starts out as some ampersand-prefixed something or another, then turns into a little box with numbers in it in the WYSIWYG editor.

Here's a cut-and-paste (don't know if this will show up):  

Attached is a screenshot, in case the cut-and-paste doesn't show up.