The Libra symbol (also called Libra glyph) is a shorthand representation of the Libra scales (see below). However, as with the picture itself, much is based both in interpretation and the preference of the writer, and can range from simple to extravagant.
Above are some examples of commonly used styles for the Libra symbol. Each of these is equally valid - there is no 'correct' version as long as the general shape is maintained.
Origins of the zodiac symbols and signs
The word 'Zodiac' means circle of animals (though note some signs such as Libra aren't animals in the normal sense). These 'animals' were based originally on the pattern of the stars in their corresponding star constellation. Basically what the earliest astronomers and astrologers saw when they squinted at the night sky.
Due to this although Libra will always be represented by the scales, there isn't any one 'correct' shape or design for those scales. It's a cosmic game of join the dots, and some constellations even have alternative ways to form the animal from the dots (stars).
Libra scales and balance
Any picture of the shape, concept or profile of scales or balance can therefore be comfortably used here. Designs range from the space-age to the ancient, and are limited only by the imagination of the artist, as long as it gets the point across.
Below is a representation of the Libra scales (and the Libra symbol, inset) from a medieval wood carving from the 16th century. While it's not suggested this is a great picture (hey, you try carving something into the side of a tree which will look sexy in 400 years time!) it does show how the basic concept of the Libra scales hasn't changed much over the centuries.
We have a separate article on Libra tattoos