If you want to know what products a company like Apple plans to launch, trademark filings can be a good way to find out because anyone can search them. Apple’s registration of the trademark ‘Apple Watch’ was a bit of a giveaway, for example.

But there is one way tech companies can keep them secret for the first six months, and it’s a method Apple has used no fewer than 343 times: taking advantage of section 44(d) of the US Trademark Act …

Section 44(d) says that when you apply for a trademark in the USA, your protection begins up to six months before you filed for the trademark – provided you can prove you’ve already registered it in another country.

As Quartz reports, most countries put their trademark registrations online, so they are trivial to search. But a number of countries don’t, and Jamaica is one of them. If you want to search trademark filings there, you have to fly to Kingston to perform the search in person. So what Apple does is to file its trademarks there first, wait six months and then apply in the USA.

To provide an additional layer of security, Apple generally uses shell companies to file the Jamaican applications, so that nothing is listed against its own name.

While all big tech companies do this, Apple does so more than most, says former USPTO trademark examiner Roberto Ledesma.

Some companies avail themselves of section 44(d) more than others. Apple, for example, has lodged more than three times as many foreign trademark filings as Google, the next in the ranking.

The reason only large companies do it is that it’s not cheap, according to one legal expert.

“I haven’t seen this technique applied in a really pervasive way—I think it’s quite an obscure approach,” says Madhani of Alt Legal. “It’s generally going to be used by companies with real legal resources … and the willingness to spend to protect something for six months.”

Especially as it offers no guarantee of success: there are fairly frequent leaks of trademark applications by Apple shell companies in Jamaica. This was how we first heard about the AirPods trademark a full year before the product launch, for example.

But with Apple’s legal and financial resources, it doubtless falls into the ‘can’t hurt to try’ category.