What do the black garbage bags symbolize in Chapter 2?

The black garbage bags carried by the Memory Police officers as they raid the narrator's home symbolize the intention to eradicate. It is not enough for the disappearance of birds to be felt by everyone on the island, nor is it enough for the island's citizens to tearfully release their pet birds from their cages. Only when every last shred of evidence that birds had ever existed has been collected and destroyed have the Memory Police accomplished their mission.