The significance of the title Maus I by Art Spiegelman is that the German word for mouse immediately points out the way Jews were viewed by the Germans. The rest of the title, A Survivor's Tale, points out for the reader that Spiegelman is telling the story of a survivor--that of his own father. Because Spiegelman is an artist, all the people are portrayed as animals with the Nazis being cats which hunt. The Jewish people are portrayed as mice which makes the cats' constant hunt feel much more real. The reader can visualize the mice's desperate attempts to hide or escape the traps set for them. Again, as mice, the reader can see how many ways the mice are caught, what happens to them, and how many of them survive. Spiegelman's father does survive, but lives a very unhappy life, so that even survivors are still living the memories of being hunted continually.
Part of the significance of the title is that the word "Maus" (mouse) is German, which underscores the idea that Nazis described Jews as rodents, pests, vermin. Also significant are the rest of the words in the title--"A Survivor's Tale"--This isn't about the German's domination of the Jews, it's about surviving.