While many students do it, it is certainly not legal. I know of two student projects that carried unofficial "branding" of some sort and they got into some trouble (angry calls and lawyer letters). As far as I know nothing financially painful happened, but signing a document that you will never ever use or show your design work again is tough enough (especially when it is a big thesis project, ouch).
And yes, it is a dick move (how we call it in bird language) to trouble students with that, but keep in mind that big brands usually employ a bunch of bored lawyers who will dig through the internet to specifically find infringments regarding their client's brand. They don't really care if you are "just a student". That said, you will reduce the risk to get into trouble significantly if you just don't upload your work to the internet and just include it into your pdf portfolio... or pick a brand that is too small to bother wasting resources on that kind of stuff.
Also I don't really know the legal situation in the US, it might be different... you guys also have fair use and such - some things are much stricter over here!