Julia Angwin's contention about PIN-locking the Signal app

[http://dummy.us.eu.org/robert (Robert)]

There is no way to do this with the out-of-the-box Signal app.

With the Molly.im app, a Signal-compatible app, you can.

Not sure if it's important to hide Signal chats on your phone.  If it is,
you need to install Molly (via F-Droid) and follow these instructions:

 https://github.com/mollyim/mollyim-android/wiki/Migrating-From-Signal