Phallic Art of Bhutan
This is a great introductory article describing the phallic art of Bhutan. The name of the article is "In Bhutan, friendly phalluses painted on houses scare off evil spirits (NSFW)".
The custom of painting phallic imagery on the outside walls of Bhutanese homes is believed to ward off negative spirits and protect against obstacles. Although the origins of the practice in Bhutan are generally attributed to an eccentric teacher named Drugpa Kunleg, it is more likely that the custom is far older and related to folk culture and marital customs.