This object indicates the amount of signatures replaced in last
one hour in sigblock. DRE stores the metadata (chuck signature)
in signature block of DRE cache. If new signatures have to be
stored in the cache, the older signatures in the sigblock are
evicted in First-In-First-Out (FIFO) order. This object would
also indicate how much new signatures have been stored in the
DRE cache sigblock in the past one hour.