Contrary to some rumors, Voldemort didn’t set up a Taboo during the First War; he didn’t have the Ministry access to do that yet. Instead, he trademarked his name and made a deal with the goblins (who will deal with anyone as long as they get a cut of the profits) to charge anyone who used it without his permission a small fee, to be transferred automatically from that person’s vault to one he set up for this purpose. Within a few weeks (filled with splashy, headline-grabbing raids and attacks), he had enough Galleons to fund the entire Death Eater operation even without his pureblood supporters’ money, and the entire country was calling him He-Who-Must-Not-Be-Named.

After he was vanquished by a baby Harry Potter, the goblins stayed mum on whether the deal was still in effect (client confidentiality!), so people kept it up just to be safe. This is also the reason Dumbledore’s the only one who’ll say the name; he’s exempted, because Tom’s too chickenshit to steal from the Only One He Ever Feared.

…I just saw an ad for a Harry Potter game with “Lord VoldemortTM” in the text, and the sheer absurdity of it inspired this prompt out of whole cloth.

EDIT: Just to be clear, I meant for this to happen during the *first* war, before the books take place. Obviously he goes ahead and sets up a real Taboo once he takes over the Ministry in DH.