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