When a search set contains a resource, that resource will often have references.  Typical behavior is to perform a 'read' to retrieve the referenced resource.  However, if there is a need for a signature on all data retrieved, then a read is insufficient.  (There's no support for signatures on reads.)

The specification should indicate that a client can transform a resource URL into a search by changing [resource]/[id] into [resource]?_id=[id] and retrieve the results as a search (with a signature)