The origins of the Alfa Romeo badge and the serpent (biscione) as used originally by the City of Milan have been discussed on here before. If you do a search you'll find lots on this.
The authoritative source on the origins of the Alfa Romeo badge may be found in Peter Hull's book 'Alfa Romeo' (Published by Cassell, 1964). Here follows a summary of the research discussed in this book.
Both elements of the badge (the Red Cross to the left, the serpent to the right) as used as emblems of Milan have their origins in the First Crusade of 1096. All armies fighting for the Christian cause in the Holy Land (England, France, the Italian States etc) wore white robes to reflect the sun, the Red Cross being added as the symbol of Jesus Christ, the red representing the blood shed by Him to save us all. When the armies of Milan returned home the City State of Milan (being an independent sovereign state ruled by the Duke) adopted the Red Cross on a white background as its official emblem (known as the Red Cross of Milan).
The serpent to the right is even more interesting. This represents the serpent that Moses was commanded to lift up in the camp of the Israelites in the Old Testament story. A Bronze replica of this serpent was made and kept at Constantinople, and was brought to Milan by Archbishop Arnolfo in the early 11th Century, before the First Crusade as mentioned. The Bronze Serpent is still kept in the church of St Ambrigio in Milan today. The ruling Visconti Dukes of Milan quickly adopted the symbol of the serpent as a personal emblem, and added their ducal coronet over the head of the serpent. It is this personal symbol of the Visconti Dukes that was directly copied and used to the right of the Alfa Romeo badge (the Red Cross of Milan also being adopted to the left).
However, we must keep the best till last. When the Milanese army battled successfully in Palestine, they also flew the Visconti badge of the serpent as they went into battle (they were paid mercenaries of the Duke). The symbol was potent as this being an Old Testament symbol, the Muslim saracens too would recognise it (as the Muslim faith recognises the Old Testament, but not the New Testament). The Milanese army then decided to add the devoured human to represent the destruction of the Saracen armies and the Muslim faith in favour of the Judaic Old Testament (the serpent) coming in turn to the rescue and recovery of the birthplace of the Christian New Testament (the Red Cross of Jesus Christ).
Something to think about when you next polish the badge