re: ...what if I just want random letters to appear in circles as superscripts?
How random? Presuming that you are on a version of FM (8+) that sort of supports Unicode, and you have a font available that populates the Enclosed Alphanumerics block, and all you need is a-z or A-Z, then you only need to know how to apply a Character Format (if necessary), and type arbitrary Unicode code points, like U+24D0 (circled a).
A couple of things that won't work are: doing these characters as autonumbers, or doing them as ordinary letters followed by the Unicode combining circle U+20DD (unless later versions of FM have more Unicode support than I'd guess).
Plan B is to create an anchored frame (at insertion point) with an elevated (superscript) vector art circle (SVG or EPS), and text box within it, containing the letter. This could be an autonumber, but perhaps more usefully, could be an Xref, perhaps to a callout number elsewhere. I've used this hack on pre-Unicode FMs.