Legally speaking, it's not DOT compliant and unenforceable. So you don't have to stop at all. And if you want to, you can actually file a complaint and have it taken down. Traffic control signs must be approved and provided by the city/county.
Anecdotal: I filed a complaint when neighbors erected a speed limit sign in our neighborhood and put a camera on it. They were told to take it down or it will be forcefully removed and they'll be fined for the time and labor involved. It was removed about two weeks later.
This happened about 4 years ago. I did sit and think about where I would have a copy of this photo. I couldn't find it. That said, yes it was a homemade sign. Wooden post, speed limit said 15 and it was overall about half the size of a real DOT one.
Lots of neighborhoods have a nosy neighbor that always get into everyone's business or tries to police others. Grateful I no longer have to deal with someone like that. If you've never dealt with someone like that, I hope you never have to.