@MsMerope at least for 1:1 chats it looks like the message was sent but never received (i.e. one checkmark, not two). Whether this is due to network outages, the user not using the app anymore, Signal server issues or being blocked is indistinguishable.

That is what they see (one checkmark). Whether people can reasonably infer why that it's a block is is a different story. But you can always say "I never got it" and it's consistent with what the other side sees.