What if the seller is not from the US? What if he is from an European Union member state?
Patent Application Attorney
Yes. This would likely infringe on both the trademark rights and the copyrights of DC Comics. In short, you are trying to trade off of a very famous logo by creating a derivative work. It really does not matter where the infringement takes place. If the goods/services are to be sold in the US, then US rights provided to DC Comics will be problematic for this seller.
The answer to this question is for informational purposes only and does not form an attorney-client relationship.
Contracts / Agreements Lawyer
Yes. it is likely trademark and possibly copyright infringement depending how it is done. If you use this on a commercial product expect a C&D letter from DC.
Doesn't matter the location of the parties, in fact it might make it easier for DC if you are shipping from the EU to the US. It can be seized at the border by customs if DC files the proper paperwork.
Intellectual Property Law Attorney
To get a feel for the designs that DC Comics believes either infringes or dilutes its “S” Superman mark visit the link below and click on the serial number after the “S#” in the second column entitled “Defendant(s), Property(ies).” You will discover that DC Comics very actively enforces its famous “S” Superman mark. It would not be wise for you to alter it and then sell that altered version.
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
This would be clear, blatant trademark infringement and copyright infringement. It is irrelevant if the seller is located in Europe (except it may be a little harder to sue him in the U.S. and enforce a judgment for damages). Further, if you are located in the U.S. and you purchase goods containing such altered logos, you are engaging in illegal counterfeiting and you can be subject to both civil and criminal penalties.. This is a terrible idea from the point of view of both the buyer and the seller.