Every day we interact with objects, places and sensations that affect the way we think and feel. This can be used to the writer's advantage by planting symbols in the reader's path to reinforce a specific message, feeling or idea.
Look at the setting and the character's state of mind, and then think about what you want the reader to see. Is there a descriptive symbol or two that works naturally within the scene to help foreshadow an event or theme, or create insight into the character's emotional plight?
Fangs & claws
A snake's hiss or the rattle of its tail
Blood and feathers on grass
Torn up earth
Animal cries of pain or terror
Animals fighting over territory or dominance
The shriek of a bird of prey
A snarl or growl in the shadows
The tide during a storm
Animals fending off predators to protect young
A ransacked nest with broken or missing eggs
Claw marks and upturned earth around a burrow
Violent crimes (murder, home invasion, rape, etc)
Escalating verbal abuse
Broken windows & locks
Kicked in doors
Guns, knives, brass knuckles & other weapons
Sporting event fights (hockey tussles, boxing, street fighters, cage matches, etc)
Cruelty to animals
Violent video games, movies
Hit men, assassins, loan shark 'muscle'
Modern Pirates, Sex Slavers, Human Trafficking
Fistfights, shoving, bullying
Black eyes, bruises, split lips
These are just a few examples of things one might associate with Violence. Some are more powerful than others. A slaughterhouse is a strong symbol, and likely will not require reinforcement. However, a single uprooted tree may not foreshadow Violence on its own. Let the story's tone decide if one strong symbol or several smaller ones work the best.