The Big V is the highest honour medal Vorticons can award. Keen received one from the Vorticon King as he freed the Vorticons from the enslavement of Mortimer McMire. The medal is golden and rather large, as can be seen in the picture on the right. The medal has the letter V inside a circle. The V probably stands for Vorticon.
It is somewhat interesting that the letter V should be in the Roman alphabet, as opposed to the Standard Galactic Alphabet like the rest of the signs on the planet. It is possible that a special version of the medal was made for Keen.