Once used the old 'like' feature for a site makeshift bookmark feature.
I'd say could be done now with 'reactions' quite easy.
A 'right now instant' way would be to just 'react' to the comment and then view profile later to revisit
Or perhaps invision or an app dev could take it further by adding a simple 'bookmark' reaction and a separate 'bookmark' display on profile all contained in the existing feature