Who gets Y stock symbol?

Looks like BRK’s acquisition of Allegheny will happen.

Allegheny’s stock symbol is Y.

Not too may companies have a single character stock symbol. So presumably there is some cachet in owning one of them.

Just curious, what is the process of allocating the stock symbol from one company to another?

Who “owns” the rights to the symbol? Do they auction it off or just allocate it to another company who asks for it?