Two leading men of hip hop, Bryan "Birdman" Williams" and his brother Cash Money Records founder Ronald "Slim" Williams, are going into the oil business. And Birdman has a new tattoo of an oil rig on his head to prove it. They've started a company called Bronald Oil & Gas LLC. One bank told its clients last week that their arrival might be the sign of a new market rally. “Doctors and dentists investing in oil wells was sign of top in 1980s,” the bank said in a note. “Rappers the sign this cycle?” The new venture's Web site says it will explore and develop assets in the Gulf Coast region and Oklahoma. Cash Money counts Lil' Wayne as one of its rappers.