16 bit signed data format in PMBus spec

The PMBus specification (>= Rev1) specifies that the query command returns a data byte with a binary bit pattern of 001 in bits 4:2 if the format used for the queried command is a "16 bit signed number".

this is the only mention I can find of this data format (distinct from other 16 bit formats already covered by other bit patterns) within the PMBus standard.

What does this relate to? (AVS maybe?) Am I missing something silly?

*Note that I come at this from the device designer side rather than the host system side