https://signal.org/blog/improving-registration-lock/
This is available at the disposal of the users in addition to the randomly-generated, 30-character password.
再講,其實backup (export as database) 係個 feature, not a limitation. 我諗多數messages 都唔需要被backup, 如果有紀念價值您可以安全地 backup to Standard Notes, etc. With Telegram 你之不過係transfer trust from a cloud server to another cloud server.
多數其他messaging apps都會直接save落 Internal Storage 或雲端儲存度, Signal 則唔會, 除非你explicitly咁做.