HOLY SYMBOLS

When I picked my student Sharveen up this morning on the way to school, he noticed the symbol drawn by the priest during the Car Pooja yesterday. He informed me that the symbols represented the holy spear of Lord Murugan and the Om sign. According to Sharveeen, the Goddess Parvathi gave the Vel weapon to Lord Murugan for war. The Vel, or sacred spear, is the most powerful weapon in Lord Murugan’s armoury. Having it drawn on my windscreen would signify that it will protect me from harm's way.
As for the Om symbol, I did a quick check on the web and got the following info:
Om or Aum is of paramount importance in Hinduism. This symbol (as seen in the image on the right) is a sacred syllable representing Brahman, the impersonal Absolute of Hinduism — omnipotent, omnipresent, and the source of all manifest existence. Brahman, in itself, is incomprehensible; so a symbol becomes mandatory to help us realize the Unknowable. Om, therefore, represents both the unmanifest (nirguna) and manifest (saguna) aspects of God. That is why it is called pranava, to mean that it pervades life and runs through our prana or breath.
Source: http://hinduism.about.com/od/omaum/a/meaningofom.htm