I should not guess what @asugar hopes to get, but perhaps similar than all other webpages — and WordPress mostly uses: navigational breadcrump builded using categories.
But Discourse has only two level deep construction so it can be only home - category - subcategory (sure, there could be page number too, but that is useless and I reckon almost impossible to build).
So, a breadcrumb doesn’t give anything else but eating space.