In less than a month, Austin Tex-Mex staple El Arroyo  has sold so many copies of its first coffee table photo book, a collection of some of its most popular marquee signs, that it can barely keep up. In fact, if you were hoping to give one as a present this holiday season, you might be out of luck: the book is now on back order.

“I thought we might sell a couple hundred, but once we put it out there, we quickly sold thousands and are now on our third run of printing” says Ellis Winstanley, who co-owns the 30-year-old restaurant with his brother, Austin. The joint of course is famous statewide and beyond for its parking lot sign, which offers a daily dose of comedy for commuters along Austin’s busy West Fifth Street, displaying witty commentary on everything from politics and local news to Beyoncé and queso, with black block letters that are changed out each night. El Arroyo’s Big Book of Signs Volume One features 158 photos of the restaurant’s best work.

How do they do it? Being funny and topical on a daily basis is a team effort—and one that’s shrouded in secrecy. The signs’ masterminds include the brothers and a small group of contributors who remain anonymous. Sometimes, the signs just write themselves, Ellis says. “We pay attention to what’s going on in the world, which is usually pretty humorous!” Other times, the group uses a submission from one of El Arroyo’s passionate group of fans, which includes 92,000 followers on Facebook and almost 66,000 on Instagram.

Social media has become an integral part of the sign’s fame, spreading the word(s) across the country, and beyond. “If you care about the animals so much, why are you eating all their food?” triggered what Ellis called “a global vegan war” after a group from England found it offensive, resulting in a heated a debate on the restaurant’s Facebook page. The sign can also take a more serious turn around events like Hurricane Harvey.

Ellis and Austin bought El Arroyo in 2012, adding it to their restaurant group that also includes Star Seeds Café (which they acquired as sophomores at UT), Cain and Abel’s, Abel’s on the Lake, Abel’s North, Hill’s Cafe, and The Tavern. The book is currently on back order, but you can still order it here, where they will also soon be selling calendars and coffee mugs. In lieu of your own copy, Ellis shared a few of his favorites from the book.