This is the Saints Row 1 Tombstone. (Confirmed visually by looking at the weapon in Saints Row 1)
After looking at the SR2 tombstone again and seeing how similar they were, I had doubts so I rechecked Saints Row 1 again. But the weapon in this image is definitely the same weapon as the SR1 tombstone. It is almost completely black, and the top barrel is smooth the whole way, unlike the SR2 Tombstone.
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The Tombstone is a shotgun in Saints Row and Saints Row 2. It is carried by the Stilwater Police...