The best way I have seen so so far:
Get two wooden dowels, about 6" long, and drill holes in the center, crossways. Then get some thin guitar string and thread it though and twist/tie it to each dowel. In the end you want to have the thing that bad guys always strangle their victims with in the movies. Anyway, put it behind the badge and drag it through the adhesive, while pulling out to keep the wire against the back of the badge and not the paint. Then clean off the glue with adhesive remover and maybe a heat gun.