That's why it's not about anything, why it is not a vehicle for communication, not a true language. The magnet has ceased to exist. I don't think mathematical expressions are completely devoid of meaning. I think the notion of meaning is a little broader than you see it. We don't need to put it into any specific context to fully understand the message that it conveys.
Formal language is nothing else but a set of codes used for coding and decoding real language.
It is just another way of expressing a meaning. And the fact that both the sender and the recipient understand the formula in the same way is another proof for its meaningfulness. But the expression DOES contain a knowledge about a relationship that is present in the real world, although this meaning is highly structurized and conventional. Yes, a meaning can not exist without a corresponding knowledge expressed in words of a human language. But the mere fact that mathematical language exists is already a proof that it is meaningful.