The lime, chillies and piece of charcoal hanging from a string is a charm used to ward off evil/bring good luck (to a business, especially). You'll find them hanging at the threshold of even the most modern and trendy shops, and also under the front bumpers of goods trucks. I have seen it in use in domestic situations as well, though not as often as a string of mango leaves and flowers (usually marigolds). The word underneath it, Amul (pronounced "uh-moul") literally means "priceless" -- it's also a brand of butter and dairy products, and hence its presence on a sign at the top of a shop.