The sign is two months old, it was hung in a few shuls around town and removed within a few hours. I haven't seen it hung in any Shul personally and I've been around.
A couple of the signatories are most definitely anti-vax, and have been since before the vaccine came out.
Several of them (R' Stein, Klein, Halberstam, Reisman) wrote explicitly that they don't know the inyan well enough but because some people are screaming about the danger it's good to ask your doctor or to stay away for now until they do more research. One (R' Bittersfeld) appeared to water down his signature as well.
Two of the signatories (R' Zimbal and R' Blumenthal) have advised people I know to get vaccinated recently so something is up. I'm not positive but I'm pretty sure another one (R' R Halpern) has advised others to vaccinate as well. R' S M Katz who I think is widely considered anti-vax told someone who asked if they should take the vaccine that it's fine if they do, fine if they don't. Even R' Shmuel Kaminetzky (!) advised seminary girls to take the vaccine to get into Israel.
There is definitely something missing which is probably why it has not received more attention (many people haven't seen it and it's been around since Elul).