I always found them annoying in the first place.

Back in the day when forums were mostly listservs, they made sense as the sig was where you stuck your finger info, so others could look you up.

But once things switched to real forums with user profiles, the original purpose was redundant as that information could be found linked to the username. So people started cluttering them with little digital billboards instead.

At that point, it served no real purpose and wasted data and (with the advent of mobile browsing) screen real estate.