Bollocks.
But that's because it's illegal to import counterfeit goods. So that's the crime there. And it's investigated by customs officials, who actually have the power to enforce the law. But in practical terms, unless you're bringing through large quantities of fake goods in original packaging with labels on, and are obviously looking to sell them, they're not going to do anything.
In terms of bringing legitimate products into a country, then yes, for high value items you have to declare them so that you can pay import duty on it. And again, failing to declare something is illegal. Simply owning a counterfeit watch is not (in the UK at least).