No, aslong as you know what both of them mean.
I hate when peole preach or support things they don't know one thing about.
Like, in System of a Down's "Chop Suey" the lead singer quotes what Christ said on the Crucifix when He was dying: "Eloi, Eloi, Lama Sabachthani?" translated to English as "My God, My God, why hast Thou forsaken Me?" Christ also said "Father, into Thy hands, I commend My Spirit." However, the lead singer says "Father Dearest, I commend My Spirit," which for one, quoting Christ while He was dying is sacrilegious in itself, but in the video for the song, you see all these people in the crowd singing and singing along to it, when you know damn good and well they don't know what the fuck they're talking about.
Stuff like that gets on my nerves. Not you wearing The Star of David and A Cross on the same chain, as long as you know what they mean and you respect Them.