Definition:
Legend has it that there was once a gun that gave the owner status, certain power etc., but not without extracting some terrible price from that person. As a result, no one person could or would hold on to the gun for very long. It would be passed from person to person, bringing fortune and misfortune.
Now it has come to mean something that is passed from person to person quickly because it brings bad luck.
Usage:
That house is the dead man's gun of real estate.
Explanation:
The story likely arose to demonstrate the folly of doing anything for fame and fortune. The gun in this case is the latest embodiment of ages old advice, ie., be careful what you ask for, you might just get it, or do unto others as you would be done unto etc.
Trivia:
HBO, a US network, made a TV series called Dead Man's Gun.
