AFAIK it is not possible to format list item. Anything you'll find re conditional formatting or whatever, applies to the displayed value, which I think is not what you're asking for. I have read that there is/was an ActiveX control called ImageCombo with which you could display small icons to add a bulleted effect but I'd caution against using any non standard Access control. Other than that, you'd have to fake it with a small continuous form or something similar. A lot of work for little payback IMHO.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.