When most think of symbolism, they think in terms of deciphering imagery and yes this is true to a point. Symbolism can be found in many mediums however, you just have to know what to look out for. Yes you'll find symbolism in images and art, but you'll also find it in cinema, books and music via allegory.
Many musicians have hidden means within their music, they do this to maintain mainstream appeal, while those with ears to hear can ascertain deeper meaning. Many books also hide deeper meaning and symbolism in allegory and esoteric ways, whereas most would only see the external exoteric words. Movies are yet another viable means delivering symbolism often overlooked by the lot of humanity.
When most think of music with occult themes, they jot to the obvious (heavy metal, extreme metal), but there's a good deal of esoterics hidden in blues, opera, jazz, hip hop, classic rock e.t.c... as well. Led Zeppelin is a prime example of this!
Books for example, often hide meaning through allegory, this much were taught as children reading things like the tortoise and the hare. Words help paint a picture, but much like a classical painter, there's often more behind what catches the eye. Classical fantasy novels are notorious for this, take the lion witch and the wardrobe... the lion is an allegory for jesus (the books were written by a Christian author).
Movies often use subtlety to hide symbolism, such as all of the clocks in a film having the same time, or images hidden in the background, whereas most attention is paid to the foreground. Music videos do much the same...
This doesn't even account for the fact that symbolism is sometimes so subtle, that it's percieved only on a subconscious level. The conscious mind is perhaps 10% of our brain, the rest is governed by our subconscious!
Symbolism is there, all around us for those with eyes to see and ears to hear. It inundates us daily, whether we recognize it or not, and challenges us to look more thoroughly at what we allow to influence us on a day to day basis.
Reverend Frederick Ambrogio