Symbolism is very important in the Tantric world (as are statues depicting Tantric rituals). There are several symbols (and objects with symbolic meaning) in particular that are seen as having ultimate importance for Tantric followers:
Yantras: A geometrical drawing or configuration, a yantra is considered to have a sacred meaning because its pattern represents a deity.
Kapala: Used as a bowl to contain food or liquids to be offered in a symbolic sacrifice, the kapala is a skull cup. In ancient times, the kapala was actually made from a real human skull. Eventually, though, it became more common for it to be a cup that was simply fashioned to look like a skull.
Mala: A string of prayer beads, similar in appearance to those used by people of the Christian faith, a typical Tibetan mala would have a minimum of 108 beads. A Tibetan Tantric would often clutch the mala while meditating or reciting his mantras.
Vajra: One of the primary Tantric symbols, the vajra is generally believed to be a combination of a scepter and some kind of weapon. It represents the quality of being strong and indestructible.
Bells: The bell is used in many Tantric rituals as a sound effect. The bell and vajra are often used together, one being held in each hand. In this case, the vajra represents the male form and qualities like strength, while the bell represents females and wisdom. While the vajra and bell both have overall significance as a whole, each component of these symbols also has individual meaning. For example, the vajra's sixteen lotus petals represent the sixteen modes of emptiness in Buddhist beliefs.
Swords: Swords are very common in Tantric symbolism. They represent the ability and strength to cut through negative things like resistance, obstacles, or ignorance.
Khatvanga: A ceremonial Tantric staff, the khatvanga is also sometimes depicted as a magic wand; it symbolizes magic powers or enlightenment.
Bumpa: This is a vase used in traditional Tantric rituals such as initiation ceremonies and healing rites.
Tantric Gestures: Specific gestures hold great symbolic meaning in the practice of Tantra. These ritual hand gestures are called mudras, and involve positioning the hands in specific ways that represent things of important sacred meaning.
Mandala: A sacred circle in which the universe, a palace, or some other type of paradise is depicted, a mandala is frequently embellished with jewels or precious metals. Or, mandalas can be made from grains of sand, formed into intricate designs, in a very time-consuming process. Tantrics would often focus on a mandala in order to concentrate during meditation.
To learn more about important Tantric symbols and the history behind them, check out The Encyclopedia of Tibetan Symbols and Motifs, by Robert Beer. The author — a British artist who specializes in Tibetan works — does a great job of illustrating various Tibetan and Tantric symbols in categories like nature, animals, and weapons.