Just a note that the flatpak is not made by the Signal Foundation, it is maintained unofficially by the community. See the last sentence on the app description on Flathub:
This flatpak is maintained by the Flathub community, and is not necessarily endorsed or officially maintained by the upstream developers.
There’s a discussion about the community flatpak’s trustworthiness on their repo here and here, a feature request for the Signal Foundation to have an official release here, but for now the only official Linux release of Signal is for Debian-based distributions.
You may like this pattern of starting all custom commands with a comma - benefits against a wrapper command would be shorter command names and built-in tab completion.