The third symbol is a cross because Jesus Christ, who is both God and human, makes a way for us to be with God again. Jesus is perfect because He is God, and he died as a human to pay the price for our sins. Bur Jesus didn't stay dead for long. Three days later, Jesus rose from the dead and appeared to many people.
Because Jesus paid the price for our sins, He can offer something no one else can: forgiveness of sins. Sin is what separates us from God, and removing sin is how we can get back to a right relationship with God again.
The last symbol is a question mark because the most important question ever is this: Now that you know this, what will you do?
Will you accept Jesus's free gift of forgiveness from sins, a right relationship with God, and spending eternity with Him?
Or wil you ignore the gift and not have this relationship with God?
The choice is yours.