Hello,
"signal-desktop-bin" is a binary based package. It's using Signals official APT packages and packages the provided prebuilt binaries.
"signal" on the other hand directly builts signal-desktop from source
Given the fast moving JS/Electron community and possibly breaking builds due to incompatibilities of signal-desktop's code with the latest arch build dependencies, I suggest keeping the -bin package for an easy to use, quick installing alternative to the source build.
The `-bin` suffix is widely used in AUR so I suppose most users do understand the implications.
PS: There used to be a third signal package in AUR - "signal-desktop" - it was recently deleted. It also was building from source so more a duplicate of "signal" rather then "signal-desktop-bin.