I OJT'd as a 13F, I think it was a different MOS back in the day, this was in the mid-80s when I was stationed on Ft Sill, at the time whenever any unit went to the field with the boom-boom battalions they utilized everyone as a FO for back-up, and even though I was a 95B at the time, it was an interesting thing to see and learn, I think that it would be a good certification recognition, but not really worthy of a badge as we have too many now as it is.
Let me elaborate, if we give a badge for each individual field for expertise, then it would apply to all, because I am proficient in drug interdiction and investigation would I be able to have a special badge for drug identification or investigative skills, I don't think so, it is part of my job, just like it is for a 13F, part of the job.

Artillery
Joint Fires Observer
