I don't think it's necessarily pride, but just a way of identifying with a certain group. Traditionally the fish symbol was used by early Christians as a way of identifying each other and I think that's the intent now, although I'm sure there are a number who use it as some kind of backward status symbol. From another perspectice, who really gives a stuff why they do? Your question suggests that anyone who displays any kind of branding or loyalty is showing 'pride'. You really don't have the understanding to judge the motives of others be they Christian or Non-Christian. The fact that you are making such harsh judgements based on a bumper sticker is quite ridiculous. Relax!