'The Sons of Anarchy' "club" talked about the L.A.-based bikers known as the "One-Niners". Here's what the wiki for 'The Shield had to say about this fictional gang of black bikers:
The One-Niners is an African-American gang that is central to the plot of Season Four.
The One-Niners were the target of coordinated efforts by Captain Monica Rawling to bring them down, using asset seizures and court injunctions, [and by] using an Anti-Gang Task Force coordinated by Vic Mackey.
Toobworld doesn't really need anymore than that to establish this as a link between 'The Shield' and 'The Sons Of Anarchy'.