The history below comes from
www.homdrum.no/alfa/alfahistory_logo.html. There are many other versions, but this one is pretty much the going story on the badge:
"The logo is split in half and contains the emblems of Alfa's hometown Milan and the one of the great Milanese 'Visconti' family.
On the left is the red cross on a white background, which refers back to the days of the First Crusade, when many Milanese soldiers were amongst the Lombards who followed Giovanni of Rho to the Holy Land. The red cross was their symbol, whilst the white background symbolised the white shirts they were forced to wear under their armour to protect them from the fierce Palestinian sun.
On the right of the badge are the arms of the Visconti family, which later became recognized as those of the City of Milan.
There are several stories on were the serpent came from. Some says it represents the snakes that the Lombards used to wear round their necks in a little case as a lucky charm, - or the dragon which, at the start of the fifth century, plagued Milan and was finally killed by Uberto, Squire of Angera, and founder of the Visconti family, - or it could be the symbol of Ottone Visconti who fought a victorious duel with the Saracen leader, Voluce, during the First Crusade (this is where it is said that he took the shield of Voluce and used it as his own symbol - Alex Csank). The city of Milan, however, claims that the serpent has nothing to do with the Visconti family.
What's certain, though, is that the Visconti family emblazoned its red cross and serpent coat of arms over the great door of Castello Sforzesco in Milan - and this is where the Alfa Romeo association begins.
Essentially, the Alfa badge consisted of the emblems of Visconti and Milan reversed and placed on a circle instead of a shield. Surrounding the circular motif was placed a dark blue ring containing the inscription 'ALFA' at the top and 'Milano' at the bottom. Completing the badge was a Savoy dynasty knot on either side of the blue ring, separating the wording.
When the famous P2 Grand Prix cars won the first ever World Championship in 1925, the badge was encircled with thick silver laurel leaves in embossed metalwork. Over the years, these leaves lost their prominence and became less luxuriant, and when the monarchy was abolished and Italy became a republic, the Savoy dynasty knot was replaced by two wavy lines.
In 1972 the whole badge was simplified to what it is today. The word 'Milano' was dropped following the opening of the Pomigliano factory in the south - and the manufacturing of the first Alfasuds."