Grand jury subpoena for Signal user data, Central District of California
The subpoena is from Homeland Security Investigations at LAX airport.They deal specifically with crimes that involve international transport. So this is human trafficking, drug smuggling, money mules, etc.To be honest the rest of it is just standard "we have some phone numbers" boilerplate. Same thing was probably sent to Facebook, Twitter, etc. with the hopes that someone was dumb enough to login and check their messages from a burner phone.Edit: Rereading it, this is a grand jury. They likely already know the who, what, why, and how. Signal's response will go to support other evidence that they may have recovered from cell phones or cell network. Grand juries historically result in a 95%+ chance of indictment so this isn't a fishing expedition.