Bem bom is a portuguese set-phrase which would be translated as "well good" in English.
It is used to express something really good. This is very often applied when talking about food, hence this brand being a restaurant. The use of a portuguese expression gave some personality to the type of meals this restaurant would prepare - a mix of fast and traditional portuguese food. This could be a little spot in a city's downtown giving customers a way of experiencing a bit of the tastes of Portugal in a familiar way.