I think Signal should just create a pin option like how discord and a lot of others have.

But in the meantime if I had to genuinely suggest a method without any friction if you are okay with using code like the author did, then I'd suggest something and lemme know what you think

Why don't you just create a special emoji that would only be used for the purposes of Pin, like (Oh the irony), and then have a signal cli or signal-bot https://github.com/signal-bot/signal-bot where you could do something like /pins and it would show the pins but you would need a different mobile number or account for that and honestly just a big hassle. I could think of other ways but we would never reach the native User experience that signal could provide if it would allow pin natively

EDIT: Even a more simpler way could be if we could just search the chat emojis and we could just search <the pin emoji> and it would show it

Also I am surprised that HN doesn't allow emojis