This read-only Unsigned32, in MB, indicates the amount of signatures replaced in the sigblock over the last one hour, as older signatures are evicted in FIFO order when new ones need to be stored and the sigblock is full. An admin uses this alongside the data-unit replacement rate to get a complete picture of DRE cache churn across both data and metadata. A high signature replacement rate without a correspondingly high data unit replacement rate could indicate the sigblock, rather than the data block, is the more constrained resource.