Do you normally inject in the same area? If so, it could be old blood from a previous injection that has infiltrated around your previous injection area. Brown liquid is either old blood or pus from a infection. Since you didn't mention if the area you injected in was warm, hot, red, painful to the touch, or swollen, I will assume all is normal and this is probably infiltrated blood from a previous injection. But if your unsure see a Dr. and don't let them write down anything about AAS use, especially if you use insurance.
L8R, J