Dig into traditional painting, poetry, architecture, opera, traditional fahion, any art piece that heavily rely on symbolism to condense the message, and you'll get a lot of inspiration. Flowers is always a good pick. In Effy, I made one episode using floriography only (symbolism of flowers) to describe decision making (odd, I know):
Now the problem with symbolism is that the message can get lost if your audience doesn't have the same background. So if you already have a clear idea on your audience, you can also dive into classics of that particular group.
If you're tageting at rebirth, which is a natural process, nature is a good starting point. Anything surrounding spring (so weather, flowers, seed, growth), anything surrounding birth (you can add in religious elements here, from nativity to reincarnation or yin/yang), anything with flow (river, thread, smoke...).