A.M. Beer is a brand of drink which appears in GTA IV locations such as the Triangle Club. It is likely a parody of Japan's Asahi Beer.
"Asahi" literally means "morning sun" or "rising sun", and "A.M." of course means "morning", while the background of the label is similar to the Rising Sun Flag of Japan. The beer pump labels include the characters 生 ("nama"), meaning "draft", and 辛口 ("kara-kuchi") meaning "dry".
See also
Other beers in GTA IV include: