FWIW I think that Hubzilla, Streams, and Friendica are the only projects using LD-signatures regularly. But we're also the only projects with private relayed assets. Mastodon uses them rarely. I don't think anybody else uses them at all.
I'll see if I can fix this on our end, but I'm not spending more than two days on it. It's throw-away work and is just taking time away from getting rid of the darn things.