Sorry, but that's rubbish.publicity stunt: the people signing are those in control of the business and engineering teams creating the AI system. they can just stop development.
It's signed by a lot of people, some of whom are in control of some of the businesses in the space. There's no single company with a monopoly that can just decide to stop.
There's a massive land grab / arms race, so an individual company pausing development will just get left behind. What the signatories believe needs to happen is for everyone to stop/slow down to give time for the ethical framework and other important aspects to get ahead of the technology which is arguably advancing too quickly to be done with the correct controls in place. Their point is that if the industry can't collectively and voluntarily control the pace, it will need government intervention.
Anyway, do you really think they'd want people to know that they (a lot of the people involved in creating the technology) are worried that it's becoming a danger to humanity?
Before you tell me that all publicity is good publicity, just ask Gerald Ratner.