Mature trees play a fundamental role in nature and are crucial to maintaining good air quality in the urban ecosystem where they reduce air pollution, lower the surface temperature, and emit medicinal volatile organic compounds which combine to improve human health and mental wellbeing. From an aesthetic and cultural point of view, they are true living monuments to be preserved. In both rural and city environments, it takes numerous years for trees to become mature enough to have a significant impact on our health and the current global climate changes together with high levels of pollution in urban environments and other anthropic factors such as vandalism constitute important obstacles to new tree growth. This clearly makes existing trees, especially old growth, far more valuable than we often realize. Regardless of their artistic quality and in some instances their positive messages, graffiti are still unacceptable on living organisms, especially older urban trees. They also have a significant environmental impact due to the emissions related to graffiti that are primarily based on anthropogenic volatile organic compounds (VOCs) which contribute to the formation of ground-level ozone. We reviewed the literature on graffiti and paintings applied on tree bark and ultimately found that oil-based paints in particular can damage tree life support systems. We herein also discuss graffiti prevention, the potential impact on human health related with graffiti removal, as well as methods for tree bark cleaning including, as suggested by different urban forestry specialists, the application of citrus-based products for 20–60 min before rubbing and rinsing or multiple 1–2 h treatments, in the case of recent or old graffiti, respectively.