What did Annemarie mean by now think that all of Denmark must be his guard for the Jews?

Annemarie is referring to the fact that there is no one to protect the Jews from the Nazi invaders.... no one but the people of Denmark, who must act as their guards.

She turned to her father. "Papa, do you remember what you heard the boy say to the soldier? That all of Denmark would be the king's bodyguard?" Her father smiled. "I have never forgotten it," he said. "Well," Annemarie said slowly, "now I think that all of Denmark must be bodyguard for the Jews, as well." "So we shall be," Papa replied.

the button shop was closed and there was a__________ on the door a sign writtin ________________