When Omar leaves at the bus station and says goodbye to McNulty, he is asked about New York City. He replies 'There must be something happening, it's too big a town', a line lifted from the Steve Earle song 'New York City'
In his meeting with Omar, Stringer uses the phrase "truth be told" which is also the title of the guide book on the series.
In the scene with Kima Greggs and her girlfriend Cheryl and the girls drinking in the bar, Kima is drinking an Australian "Fosters" Brand stubby of beer - obviously an imported beer in Bal'more.