Ninjas are quiet and avoid being seen.
The worst thing a Ninja can do is to stand out. They don't want to draw too much attention to themselves. They only want to cause enough noise to get the job done, and not cause a ruckus. The goal is to draw only as much attention as the mission requires, and get close to the target without making it know that the ninja is there.
When we talk to people about God and Christ we should avoid being seen. How is that possible? Remember that the Bible is about Him, not about us. When we tell people what Jesus has done for us, we need to be careful not to get too caught in the "us" and forget about Jesus' part. We shouldn't be the center of that story, even if it's about our salvation or testimony. Share it and be proud of it, but put the emphasis on what Christ did, not what you did. Don't be loud, obnoxious, or "in your face" to someone, as this could distract from the message you are trying to share. That message is about God's love and Jesus' sacrifice, not about you. Tell what God has done for you, but put the emphasis on Him, not yourself. When talking about Jesus, be as stealthy as a ninja.
He must become greater; I must become less. (John 3:30)