This is the slogan
of the Original Tommy's
World Famous Hamburgers in Los Angeles
, instructing their patrons to forsake the evils of the imitators.
That's the short version. The longer version involves the story behind it.
See, everyone who's been to Tommy's knows all about their food and how wonderful they are, especially if they've been to the store in Los Angeles - the shack, as written in the title. So they all know about the shack, and know of the imitators.
On the other hand, there are apparently those that don't know a real Tommy burger from a McDonalds cheeseburger who exist. So some less than scrupulous types decided to start up their own Tommy's stores that weren't related. Little tricks allowed them to do this (e.g., you'll have "Tommy's #2" or such out there), serve their own pretty dang good chili cheeseburger, and suddenly they might compete, in theory.
Hey, wait a minute. This ain't right, now, is it? Tom Koulax didn't think so, and apparently neither did his attorneys.
Yep. Legal battle time. But herein lies the problem - you have all these people who are named Thomas or otherwise go by Tommy who run a restaurant. You can't feasibly sue somebody for having the same name as you. Likewise, people weren't necessarily about to call their restaurant Thomas', for apparent fear of uncannily confusing it with a particular brand of English muffin.
Corrolary to this bit above: Albert Herring points out that "McDonalds have had restaurants run by people called McDonald closed down or obliged them to be renamed". This is certainly true, but note that McDonalds is a publicly-owned McBehemoth, and can do that simply by exerting weight (read: continuing to fight).
(The real battle came in when somebody would open up a restaurant, call themselves Tommy's or something, serve their own chili burger, and try and say they were the original. Tommy's apparently had a decent number of such issues, if their website is any indication - but apparently they've decided to stop fighting. Read on.)
So if you can't fight them with guns, you fight them with propaganda. Customers are instructed to "look for the shack" - as there is invariably a picture of the shack that serves as the company logo, with the white handscript on the red sign - or on the bags, a more colorful version of this, with red script on a white bag. See, the big icon for Tommy's is the universally recognized shack that stands on Beverly and Rampart Boulevards in Los Angeles. If you've been to the one in LA, you know the place, and our friends at Tommy's #2 can't conceivably say that it's theirs.
This has proven to be effective, apparently, since - at least, out here - Tommy's remains synonymous with this particular burger joint, whereas places named Tommys #n or Tom's Place are, while burger joints, also known for serving other product like carne asada, giros, pancakes, french toast, etc. Good by it's own right, but it still isn't the original Tommy's by any stretch of the imagination.