What versions of the plug-in and Power add-on are you using?
Assume based on your question you have Power and you know how to display the category map marker or icon and you know about the legend box that identifies the same on the map/
categories are taxonomy /hierarchal in nature . (The term Taxonomy references the WordPress category system. Taxonomy is a way to group things together.)
If I understand your question, correctly you want to show the corresponding category as text under the results. the way to show Text driven information in your results is to associate corresponding TAGS assigned to locations .
Tags are text based. If you have the Power add-on you will see a field where you can add them just below the Power section. You can also Import tags or use the Bulk actions feature under the Locations tab in SLP to add tags an assign (with the Power add-on)
Map INFO bubbles are just that, Info bubbles that use Shortcode and Css and do not pull from the Taxonomy of category manager