I stumbled on this offer available to all active, retired and veteran military personnel.
Simply fill out the form and in about three days $100 OBC will be deposited in your account.
It looks like it can be done either during booking or after the fact as I did.
This is not a scam, I verified it with my TA prior to completing the form.
https://www.hollandamerica.com/en/us/cruise-deals/community-appreciation-cruise-offers/military-appreciation-offer