Questions always arise as to whether using Catholic Symbols is really a form of idolatry. Usually for the reason that the questioner isn't altogether acquainted with what these symbols really are. We do not worship the crucifix. It's used by us as a reminder of Jesus suffering and death for our sins. We don't worship the fish. We display it as a proud emblem in our Christianity. We do not worship the statues from the saints. We rely on them to point out their wonderful lives so that they may be role-models for us to emulate.
As far back as once the Ten Commandments were given to Moses, idolatry within the Old Testament was defined as the worship of idols or images. It's the worship of anything but God that's wrong and sinful. The mere images, symbols or icons aren't the problem.
An excellent illustration of this in the time of Moses is the Brass Serpent. God commanded Moses to make this Brass Serpent and lift it high for stopping any Israelite who checked out it of snakebites. Once more it had been God who commanded Moses to make this picture. Later in history, King Hezekiah destroyed the Serpent because the Hebrew people have been burning incense into it in worship. The symbol had eventually become an object of idolatry. Begin to see the difference?
When God gave commandments regarding idolatry he meant it to be understood in the most literal form. According to the Bible, most idolaters really thought that their idols were gods. That is not so today with Catholic Symbols.