We have recently added the following to the Draft Airports Advisory Circulars page on the FAA website:
DRAFT Addendum (HRET Hand Signals) to AC 150/5210-23, ARFF Vehicle and High Reach Extendable Turret (HRET) Operation, Training and Qualifications
In addition to the addendum, we have posted a draft HRET Hand Signals Quick Reference Guide.
Comments are requested by February 11, 2019. Please visit the page to access the draft AC and read procedures for submitting comments.