Compare/Contrast traditional badge systems
Like the cumulative aspect of the scouting badges. As well, as I remember, there are a variety of 'ground floor' badges so multiple entry points. Conversely, martial arts is prescriptive in where one starts, and the path is linear. That said, the various dans of the black belt are a nice option.
Compare/contrast digital badges
Liked how the example of digital badges made at Tuesday's webinar built on the martial art model as progression is very tangible which appeals to lots of learners, and would likely help folks understand better when presented with a badge collection of what level the 'badge-ee' was at (if that makes sense).
Indeed, the variety of badges out there is interesting--though not sure what may be meant by non-learning tasks. I see some badges as more recreational rather than academic, but both are valid learning experiences. Badges that require peer evaluation, too, are cool. It's one thing to answer a set of questions correctly and achieve some hands on stuff, but the added weight of positive peer review can lend a stronger sense of achievement to a badge.
And badges of all types tend to support a community. I think to travelling days when folks had Canadian flags stitched to backpacks. That symbol had meaning for other travellers as well as locals. Too, consider gang colours/patches and the communities of practice to which they allude. Thus, there is meaning for the badge holder as a member of a community, and meaning for an observer.