P.P.S: Yes, maybe it's unethical to take someones signature design, but it will be more worse to create here patent and copyright trolls (like in real world)
The signature (which IIRC roslinpl made back in 2017) has been in use for over 2 years now. I think it is extremely clear that the intention of the signature was not to encourage people to copy it (?) and then attempt seek damages.
Personally I think this case is a lot more clear cut than Vadi2323 - you can't make the claim that stealing a signature design to promote a different service is parody.