The "death clock," which shows the number of tobacco-related deaths since the WHO Framework Convention on Tobacco Control (FCTC) negotiations began in October 1999, stood at just under the 40 million mark at the unveiling.
The WHO said it expects tobacco to kill more than 5 million people this year - greater than the combined death toll from Tuberculosis, AIDS and malaria.
"This 'epidemic' is hitting the poorest of the poor," said Douglas Bettcher, director of the WHO's Tobacco-Free Initiative.
But he added that "we do see some green shoots in some countries" taking action to curb tobacco use, such as the use of graphic pictures showing damaged lungs and other health consequences on cigarette packets.
Six hundred delegates from over 150 countries are meeting in Geneva this week to negotiate an FCTC protocol against the illegal trade in tobacco products.
The WHO said this trade is linked to organised crime and even terrorism, and it estimates that 50 billion dollars is lost in tax revenues to governments every year.