The Signal organization is not capable of doing these things. By design, the application is secure against the sort of attacks you propose.
- Signal does not collect information about its users that would enable it to determine who is a government official.
- Since Signal conversations are end-to-end encrypted, Signal does not have access to the unencrypted contents.
The way to protect against government officials misusing Signal is to not elect people who would misuse Signal to be government officials.