In the course of investigations by the Department of Homeland Security (DHS), the US public prosecutor’s office is demanding that Signal hand over names, contacts and the contents of the conversation, among other things. They got the date the accounts were created and the time when they were last online.
The official summons contains a blackened list of telephone numbers for which the requested information is to be provided. Like signal in a blog post declares that they do not refuse to comply with this request. But due to the end-to-end encryption and the logging policy of the server, you simply do not have the requested data.