[torben-friis]

Is mimicry always sign language though?

It is certainly communication, but I think there's a difference between communication and language. The latter requires more structure: perhaps grammar, a finite fixed set of predetermined words, etc.

You don't really need consciousness to communicate, since it's just transfer of information between different entities - for example, an organism could secrete chemicals that are detected by neighboring members of the species, as I think it's the case for some plants.

Structured communication might be different, as I think there has to be a something that composes the particular "phrase".