I found out from the Navy Operations Security Support Team on Facebook that there is a new edition of the Navy Social Media Handbook for 2019. It is long, and for a varied audience: Leaders, "Navy Communicators", Sailors, Families, Ombudsmen, and Navy Civilians. It informative, and worth the time to read. For most of our members, I would recommend special attention to section for Families, but there is some really interesting material in the Communicators section.
Much of the information for families echoes what is already in our Community Guidelines, the OPSEC checklist, and other OPSEC/PERSEC (Personal Security) documents and discussions on this site.
Regarding this site, please be aware that everything here is visible to the whole world, permanently. (The Internet remembers everything.) Do not share or discuss sensitive information. Furthermore, while the volunteers who administer this site and the groups try to keep an eye on things, they have no way of verifying the identity of any member, or knowing if someone's password is compromised or easily guessed. We could very well have spies, trolls, and other such malefactors. When it comes to operational matters, if they don't know they probably don't need to know.
Our no-last-names policy should not be relied on for security purposes. These days, at least, it is more to allow people to ask advice without repercussions to their sailors. If you post similar things to other social media platforms e.g. Facebook, it can be pretty easy to correlate profiles.