Hey, Zara. I see what you're doing there. That white tee with the word "Surprise" in a red box is obviously your take on cult streetwear/skatewear brand, Supreme. Much like the rest of Zara's creations, the Spanish fast fashion giant infused a bit of originality to avoid creating an exact replica of its "inspiration". In this case, it changed a few letters. The question is: Does the change from "Supreme" to "Surprise" put Zara in the clear legally? Maybe but maybe not ...
The foundation of trademark infringement is based on the following question: Does the defendant's use of a mark create a likelihood of confusion about the origin of his goods or services? In this case, the defendant would be Zara. And as the plaintiff (the party bringing the lawsuit), Supreme would have to show that Zara is using a confusingly similar mark ("Surprise" in a red box) in such a way that it creates a likelihood of confusion amongst consumers. The confusion can take the form of consumers thinking that the defendant's products are the same as that of the plaintiff, or that the defendant's products are somehow associated, affiliated, or connected, with the plaintiff.
Here, it would be rather difficult to show that consumers are initially confused as to the source of the "Surprise" tee, as it is being sold in Zara stores and on Zara's website. Thus, the average person would likely think it was made by Zara and not Supreme. However, there is a doctrine within trademark law called Post Sale Confusion. This is kind of obvious from its name, but it is when the purchaser knows the source of what he is buying but others may be confused into thinking the product comes from a different source. There is an argument that this seems plausible here.
Also worth noting: We learned last year during the Supreme vs. Supreme Bitch lawsuit, which Supreme filed against Married to the Mob (and they have since settled), that the NYC-based brand has pending design trademarks registrations that cover its logo in its entirety (think: "Supreme" in white lettering and the red box). The only potential problem (which doesn't appear to be too serious): Supreme essentially highjacked the aesthetic of artist Barbara Kruger to come up with its logo (more about that here).
However, since Kruger hasn't opposed Supreme's use of the white lettering inside a red box via a cease and desist letter or a lawsuit of her own, Supreme's trademark application is likely set for federal registration. While we know that a trademark registration does not actually establish that you have a trademark (using it in commerce establishes that), it gives you more extensive rights to prevent others from using your mark. We'll keep you informed re: that status of Supreme's pending registrations and whether they attack Zara for its lookalike tee.