Similar to the winged skull, the hourglass indicates the swiftness of time’s passage – sometimes literally flying with wings.
The hourglass is a symbol of time. Usually this image depicts time's passing and the inevitability of death. An hourglass indicates that a person's time on earth expired and implies that visitors should embrace life because it, much like the flow of the sand in an hourglass, is finite and will eventually end.
When the hourglass is on its side this indicates that time has stopped for the deceased.