I saw this sign on my way home from work. I'm not sure if this is what the owner intends but it makes me think of wordless books and bracelets. They are intended to be conversation starters to share your faith in Jesus Christ.
Black-Sin Romans 3:23 (All have sinned)
Red-Blood John 1:7 (Jesus' blood covers all sin)
White-Pure Psalm 51:7 (Jesus washes away confessed sin)
Yellow-Heaven John 14:2 (Believe on Jesus and receive Eternal Life)
Green-Grow 2 Peter 3:18 (Grow in the knowledge of the Lord)
When someone asks about the bracelet you can say, "This is my faith bracelet. The black reminds me that all have sinned and fallen short of the glory of God. The red reminds me that Christ shed his blood for my sins. The white reminds me that my confession of sins allows Jesus to wash them away. The yellow reminds me of the hope of our salvation and Eternal life in Heaven. The green reminds me that I need to continue to grow in my knowledge of the Lord."
The colors are brain ticklers to remind you of the essential points of sharing your faith. People who do well at memorizing can quote the verse and it's reference as they go around the beads.
I've heard it said that an early Christian as they were talking would trace in the sand an arch, half of the fish symbol. If the person they were talking to was also a Christian, another arch would be drawn to complete the fish as a sign to share their faith.
Here again is a sign on the side of the road to share your faith.