My $0.02...

OK, so let's consider the set of neural patterns (and corresponding artificial signals/symbols) you refer to here... the patterns that the label "Santa" can be used to refer to. For convenience, I'm going to label that set of neural patterns N.

I mean here to distinguish N from the set of flesh-and-blood-living-at-the-North-Pole patterns that the label "Santa" can refer to. For convenience, I'm going to label that set of patterns S.

So, I agree that N exists, and I assume you agree that S does not exist.

You further say:

"I'm perfectly fine with letting the word "Santa" refer to this pattern (or set of patterns)."

...in other words, you're fine with letting "Santa" refer to N, and not to S. Yes?

Is there a problem with that?

Well, yes, in that I don't think it's possible.

I mean, I think it's possible to force "Santa" to refer to N, and not to S, and you're making a reasonable effort at doing so here. And once you've done that, you can say "Santa exists" and communicate exists(N) but not communicate exists(S).

But I also think that without that effort being made what "Santa exists" will communicate is exists(S).

And I also think that one of the most reliable natural ways of expressing exists(N) but not communicate exists(S) is by saying "Santa doesn't exist."

Put another way: it's as though you said to me that you're perfectly fine with letting the word "fish" refer to cows. There's no problem with that, particularly; if "fish" ends up referring to cows when allowed to, I'm OK with that. But my sense of English is that, in fact, "fish" does not end up referring to cows when allowed to, and when you say "letting" you really mean forcing.