Broken Melons and Red Kumkum
Over the past few months I've noticed the tradition of breaking melons and smearing them with red kumkum to mark an auspiscious day. The broken fruit is left in front of a shop or hotel, and red kumkum mixed with oil and fruit is smeared near the entrance of the shop. A few shopkeepers near my place even did this on Pongal.
When I asked around I was told it's quite common in Tamil Nadu. Apparently, this is done to ward off the evil eye on auspicious days, family functions, etc. It's also done when important purchases are made like a new vehicle or home. If its a new bike or something, the bike itself will be used to smash the melon. Before going on long journeys, the melon is at times hung from the front of the car. Most of the internet searches I did on this topic turned up discussions complaining about the mess that's left on the road after this is done.
An interesting story turned up when I was looking for the significance of this. Breaking melons in this way is also done to mark the death of Narakasura, an evil demon king. The broken melon is a re-enactment of Krishna's victory over him, and it represents the bloodied head of the demon. After smashing the melon, people may smear the red mix on their forehead. This signifies the blood that Krishna smeared on his forehead after victory. Apparently in some places they do animal sacrifices (goats) so there's real blood, but most people choose this way as its cheaper and more humane. I've read that this is done during Diwali, or more specifically on Nakra-Chaturdashi or Chhoti Diwali.