I actually set up a quick Heroku deploy to help identify when people are downloading our code and running it on a different domain than ours (just sends us an email). Most of the reckless folks stealing our stuff don't identify the little bit of JavaScript I've thrown in there, and we get a lot of these alerts. It also sends us the domain the code is running on. Of course, we aren't worried as much about localhost.
The JS also replaces the content on the page, and shows a "you shouldn't be doing this" kind of alert; we've had a TON of hits on this. It happens literally daily.
We have yet to file for DMCA takedown - good plan for those who are legit stealing.
However: I have a strong opinion on these things.
Specifically, if people are stealing your stuff, see what you can do to innovate past them. Ideas will always be stolen; edge and innovation can't be stolen.
Sometimes it's legit to call people out. Sometimes DMCA takedowns are needed. Sometimes, it's time to man up and beat the system. One step ahead, and all that jazz.