Is there any stated "rule" about what can/cannot be used for that message? Such as a message that is meant to offend another member of NGA?

Probably, unless the post is explicitly addressed to someone, nothing can be done about it. For instance, if I get into an argument with you, Sandy, and I put at the bottom of my posts:
@Weedwhacker is a rotten person that nobody should talk to.
Then that would probably have to be changed or taken off because there's no getting around the fact that I'm continuing a fight between us. But the following:
People who are rotten should not talk to me or anybody else.
Would probably be directed at you (if we had just gotten into an argument), but it wouldn't be able to be proven so it could stay.

A member has done something like this to me before, but I've just ignored it. People like that are just dying to get a reaction out of someone.

And if there is someone who's reading this and doing what Sandy's saying, I say to you: grow up please. Get over it, and move on if you had a fight with someone. Either you're right or you're wrong, does it really matter either way?

@dave

I know which one you are referring to, seems both members have a contentious history. She has already blocked him from being able to t-mail her so it looks like things have gotten heated with them before. She has changed the signature now a few times it looks like. Since she is not naming anyone, there is nothing admin can do and we generally wouldn't interfere anyway unless there was some clear use of profanity or actually naming a member.
Anyone can block a member if they do not wish to see any of their posts.

Thanks for the reply, Sue; it is actually being directed at more than just the one member (myself included), but it has recently escalated between the two of them.

It seems to me that it has calmed down a bit between them since last night. They just seem to be ignoring each other, at least in the thread on which the latest argument was started.

We can only hope that's the case...

Reminder that if someone is being very disruptive in a forum, by all means use the "Report this post" button on them. If enough reports come in, they will be blocked from posting in that forum.

Disruptive off-topic posts ruin the atmosphere. Reporting a post is not about punishing the poster, it's more about preserving the peaceful and cooperative environment we have here.

Dave , Is there a way you could post this reminder(above post) in the thread 2022 Vegetable gardening .
People who want to discuss or just read are leaving because a few wont stop the personal bickering.

I do believe that red report button has worked, it can be confirmed with @dave. I don't see any new posts by that member since yesterday and they won't see that entire forum any longer.

Dave posted on the vegetable thread letting us know that the two members were banned, Sue.

Yeah, I'm barely into my coffee and just scrolled down further and saw that.