The idea in and of itself is not what is being rediscovered. Nobody is reinventing the wheel. It's whether the implementation is ergonomic and powerful that determines whether it catches on.
May just be my memory failing me or the circles I ran in over the years, but I remember the related buzzwords always being observables and streams. I hadn't seen much interest/hype in the actual term "signal" until solidjs used it and push heavily on comparisons with react hooks.
"Signal" has been used in FRP circles for some time [1,2]. The original FRP stuff was events/signals and behaviours. But I agree that JS didn't use this terminology until more recently. S.js is maybe one of the earlier ones, but that was still over 8 years ago.