Perhaps some do Filletandrelease, but they should rethink it.
Setting a trap to deliberately injure someone could have heavy legal consequences indeed, and it won't matter that it was intended to be against thieves. On occasion traps do get pulled in legitimate circumstances, such as when found floating away in the current in very deep water or getting snagged on a log boom. Not to mention the possibility of your trap being pulled by DFO Enforcement for some reason, such as because they don't think the lettering is of sufficient visibility (letters on the float don't meet the size requirement etc.). I also understand that on occasion RCMP Marine units could pull your trap if they consider it a hazard in a navigation channel etc. In either event, if the Feds were to embed a barbed hook in their flesh, they would be highly motivated to track you down for more than a little chat. With the name and phone number on the float, even the thieves may want to look for a little payback.