The campaign builds on Mars' "pleasure you can't measure" campaign. Grey has already done tactical advertising in response to stories such as the England football squad calling for emergency supplies of the chocolate bar to be shipped out to Japan during this year's World Cup.
The agency, which has its London office only doors away from the Portland Hospital where Romeo was born, is displaying the poster outside its building.
It is not thought that David Beckham has yet added a "Romeo" tattoo to the "Brooklyn" and "Victoria" markings already adorning him. However, according to reports, he has been seen in a pair of football boots sporting the names of both of his sons.
The "pleasure you can't measure" advertising campaign was the first created by Grey after it won the Mars account from D'Arcy in November 2001. Mars is owned by Masterfoods and was relaunched in March this year with a new formulation and new packaging.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.