"314.23(B)(1) Nails and Screws. Nails and screws, where used as a fastening means, shall be attached by using brackets on the outside of the enclosure, or they shall pass through the interior within 6 mm (1/4 in.) of the back or ends of the enclosure."
I'm going to take credit for the picture above. It is a common 60's vintage wiring method here in the SF Bay Area. Joe Tedesco calls it "Boston Backwrap" so you can see it shows up all over the country.
Another odd grounding method I've run into is splicing equipment grounds on the outside of the electrical box. This was a requirement from the building official in Alameda California. Apparently, a great many electricians received their trainin in Alameda and this practice shows up to this day.