kontiki wrote
If you hold and AGII (Advance Ground Instructor - Instrument) then you
can sign off someone for the Instrument written.

A Ground Instructor Certificate can have any of three ratings:
Basic, Advanced, and/or Instrument
No such thing as an AGII. Advanced and Instrument are two
separate ratings. The Advanced rating is not required in order
to provide instrument training, just the Instrument rating.

Bob Moore
Ground Instructor Certificate
Advanced Ground Instructor Rating
Instrument Ground Instructor Rating