Why can you copyright a Helloween T-shirt and not a phone model?

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With Helloween approaching, it proves that more and more people are attracted to the "Daddy's lil' monster" T-shirt made iconic by DC Comics' Harley Quinn character. What is interesting is that the logo is actually copyrighted, so most likely if you get to buy it from an unofficial online store or from someone posting it on an auctions site, it will actually be a fake. And, if discovered, the seller can be sued for copyright infringement. However, in the mobile phone industry things seem to be different: you can buy legally, with a valid invoice and warranty, phones like the Gionnee S6 or Red Mi Note 3 and Note 4. Obviously, these model codes were used by a far more famous phone manufacturer - Samsung - for its premium range of devices. So no wonder why some near-anonymous phone brands would try replicating its model codes, in the hope that their no-name products would be able to gather at least a part of the success a top brand like Samsung had. But what I'm wondering is: why can it be copyright infringement to sell a T-shirt roughly resembling that of a movie and comics character, but it seems fine to mislead people in thinking they buy a premium quality phone, when what you are selling them is a cheap, no-name one?