Why would it be? I have a Star of David pendant that I bought in Israel that is fashioned so that the Star spells out the name “Jesus.” This kind of jewelry is not uncommon, and I can see nothing wrong with it. The only caution I would offer is that I would not give such jewelry as a gift to a non-Christian Jew, unless there was some reason to think it might be welcomed (e.g., an express desire to convert).
