As you maybe discovered there is no rpm build support from the Signal team.
Yes you can compile your own version and then do that for every new release but if you are lazy like me and nor an international wanted person (like Assange) there is a simpler version to do it.
Here comes the FlatHub to the rescue, the cross Linux distribution application store :
“Welcome to Flathub, the home of hundreds of apps which can be easily installed on any Linux distribution. Browse the apps online, from your app center or the command line.”
Just point and click to the signal page.