Final answer:
The literary device in play when stones represent death is a metaphor, which is used to symbolize or represent the concept of death by using one thing to refer to another indirectly.
Step-by-step explanation:
When the stones represent something deeper than their usual meaning and signify death, the literary device being employed is a metaphor. A metaphor is a figure of speech that, for rhetorical effect, directly refers to one thing by mentioning another. It may provide clarity or identify hidden similarities between two different ideas. In the examples you've given, the stones are not literally death, but they are being used to symbolize or represent the concept of death.
An example of this might be 'The graves were marked by stones, silent sentinels standing guard over the forgotten.' Here, the stones are metaphorically used to suggest the presence and permanence of death. This is distinct from similes which compare two things using 'like' or 'as,' personification which gives human qualities to non-human entities, and hyperbole which is exaggeration for effect.