We can't say this is unexpected, especially that registering a certain trademark in the gaming industry does not necessarily mean that developers are already working on that game, but Half-Life 3 trademark was a hoax.
Valvetime.net reports that the Half-Life 3 trademark registered in late September has disappeared from the Trademarks and Design Registration Office of the European Union (OIHM).
Earlier last week, word that Valve might indeed work on Half-Life 3 surfaced when a screenshot allegedly taken from Valve's User Pick tool showed that there were more than 40 people involved in this project.
In the same piece of news, OIHM registered a Portal 3 trademark in early October, which is still up, but this is perhaps just another fake.
Unfortunately, it's safe to say that everything was created with the sole purpose of generating more hype around Valve and its products.