They have to reveal who they worship, that is the law.
4 Hear, O Israel: Jehovah our God is one Jehovah: 5 and thou shalt love Jehovah thy God with all thy heart, and with all thy soul, and with all thy might. 6 And these words, which I command thee this day, shall be upon thy heart; 7 and thou shalt teach them diligently unto thy children, and shalt talk of them when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up. 8 And thou shalt bind them for a sign upon thy hand, and they shall be for frontlets between thine eyes. 9 And thou shalt write them upon the door-posts of thy house, and upon thy gates.
This is why people wear T shirts with their idols, this is why you discover what people worship just talking to them. Are they talking about football, late night TV, a concert, or the Lord?