What it is
An instrument in development whose domain and architecture are not disclosed. It is listed here because the registry is meant to be a complete account of what exists rather than a curated one, and an omission would be less honest than a placeholder.
There is nothing further to read about it on this page and there will not be until there is something that can be shown.
Where it sits
SIGNAL is catalogued under Cognitive Systems in the instrument registry. Instruments in this group share a concern and are frequently composed rather than used alone; the related entries below are the nearest ones.
This is a registry entry: a real instrument, documented here, without a public endpoint a stranger can open. Pages carrying source excerpts and measured results are marked as such in the catalog. If you want detail on this one specifically, ask about it directly.