Previously, you had to set this setting per conversation and it wasn't very handy in case if you were taken privacy more seriously than others. From now on, you can set a global setting to make all your messages disappear after some time in every chat that you have.
How to set all your Signal messages to disappear by default:
- Open Signal Settings.
- Tap on the Privacy section.
- Tap on the Disappearing messages section.
- Pick the time period and go back.
Source: Signal blog