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?
Sun coming out behind a cloud
The warmth of sunshine
Rain on a dry landscape
The smell of rain or moisture in the air
Sighting seagulls at sea
Sighting land at sea
Babies/offspring in the animal kingdom
New Moon (Hunter's Moon)
Pink cancer ribbon
Random acts of kindness
Schools, youth centers
Light bulbs/light sources
Statue of Liberty
Church and cross
Experimental treatments/drug trials
Advances in science
The comforting arms of a loves one
New beginnings (new job, new school, new look)
Moving into a new house or neighborhood
These are just a few examples of things one might associate with Hope. Some are more powerful than others. Being given a vaccine for an illness or finding out one is a candidate for a new treatment is a strong symbol, and likely will not require reinforcement. However, an open door may not foreshadow hope on its own. Let the story's tone decide if one strong symbol or several smaller ones work the best.