[wavesplash]

There are some great opinions posted so let me add some data from uspto.gov (use 'trademark search' from the menu) and a touch of what I understand of Trademark law after filing a few myself:

53 was granted a US Trademark on the phrase 'Paper by FiftyThree' on December 2013 for trademark categories 21 23 26 36 38 and it appears international category 9 with a first-used-in-commerce claim of March 2013.

53 are obligated to enforce their mark in those categories otherwise they risk losing it. This is the same reason Facebook goes after anything with 'face or book' that even vaguely seems similar. If they don't they risk losing the Facebook mark.

The law sides with the trademark holder as long as they enforce the mark.

As many people have mentioned, 'Paper' is generic and 53 didn't get the word 'Paper' by itself. It was granted the mark 'Paper by FiftyThree'. Since Facebook's app isn't called 'Paper by Facebook' this leaves some wiggle room if FB wants to challenge the claim if it heads to court. Facebook has deep pockets and good lawyers, so perhaps they've already calculated the risk and is willing to fight in court. 53 may not be able to afford that fight (cash or distraction wise).

TL;DR: 53 is obligated to enforce their Trademark and the letter to Facebook is a manifestation of that obligation. Unfortunately their mark isn't just on the word 'paper' so it will be interesting to see if this fades away or the parties head to court.

[seandougall]

> 53 is obligated to enforce their Trademark and the letter to Facebook is a manifestation of that obligation.

But the open letter is not. A simple C&D would have protected them; publishing it is purely about marketing.

[wavesplash]

Agreed, seems an intentional move from the marketing playbook: If goliath gets news, pick a public fight when you're David. A very cheap investment for that level of exposure.