Yesterday, as Facebook launched its news reader app Paper, design-focused startup FiftyThree called out Facebook publicly for using their brand name. Facebook declined to change the name of their brand new reader app.

But FiftyThree has taken action to protect its brand name. FiftyThree’s trademark application for the term “Paper”, which was filed for on January 30 (the same day that Facebook announced Paper), surfaced today in the USPTO database.

FiftyThree CEO and co-founder George Petschnigg had previously told TechCrunch that FiftyThree is “keeping its options open.”

Using a startup’s brand name wasn’t the noblest move by Facebook, but technically FiftyThree’s only trademark in the USPTO was for “Paper by FiftyThree”. So Facebook went for it.

FiftyThree cofounder and CEO Georg Petschnigg said in an interview yesterday that FiftyThree had applied for the “Paper” trademark, on its own, alongside its already-approved “Paper by FiftyThree”.

Usually, the USPTO makes trademark applications public in search within five to seven days, but at the time of publishing yesterday we were unable to locate an application from FiftyThree for “Paper”. This morning, however, the application went live in the system, showing that FiftyThree filed for the application the same day that Facebook publicly revealed its own Paper app.

If FiftyThree chooses to move forward legally, the company has a case, according to trademark lawyers Roberto Ledesma and Victor Cardona

Trademarks, to a degree, are use-based. This means that “just by using a mark in a particular field, you’ve got rights,” said Cardona. “Some are state-based and some are federal-based, but if I start using a mark before you in the same area of goods or services, I’ve got rights to the mark over you.”

Obviously, applying for and winning trademarks makes those rights even stronger, which FiftyThree has done. But nothing is a sure thing, especially considering how subjective trademark law is. Just like use can determine the strength of trademark rights, with or without a filing in the USPTO, third-party use of that mark can weaken one’s rights over a certain word or brand name.

These factors will be weighed into any potential lawsuit, as will the differences between the companies. In terms of utility, Facebook Paper and Paper by FiftyThree don’t really compete. However, they likely do fall into the same category of “consumer software applications for a mobile device.”

“As the later user, Facebook would have to make the case that these uses are distinguishable and consumers will not be confused,” said Roberto Ledesma. “The more similar the marks the less similar the uses have to be to find infringement. Here the marks are identical so less similarity is needed.”

Here’s what FiftyThree said in response to the filing:

In the U.S., trademark rights are use-based (i.e., one does not need a registration) and FiftyThree has well-established common-law trademark rights in PAPER alone. Google “Paper” and we are the #1 result. Search for #MadeWithPaper on social media and you’ll find over a million creations in public.Indeed, PAPER alone is widely recognized by the public as our brand and trademark. And we recently filed for registration of PAPER alone. At this point we are reserving all legal options. More importantly, we stand for creativity and believe in a level playing field when it comes to building companies and brands.

Unfortunately for FiftyThree, Facebook has the resources to wear down a smaller company, who can’t afford a lengthy and expensive legal battle. Even with $15 million in funding.

And yet, on the other hand, Facebook’s new app has brought tons of publicity to the startup. It may show up second in search results, but more people will search for “paper” than ever before.

You win some you lose some?