Positive ground. In the Physics Department, we used "i" to define the current. In the Engineering Department, they used "j". Tastes Great, Less filing!
When one gets to a junction and gets a negative current answer when applying Kirchoffs's rules, it simple means that the current is flowing in the other direction. That seemed to blow people's minds. I was in an engineering class (working on a master's degree, but dropped out because of my workload at my job) back in the '80s where the instructor drew an arbitrary curve and defined the current flow as "to the right" Then he said that -i was current flow in the other direction. Some of the student's heads pretty much exploded, at that point. By the time people took that class, they should have at least had vector calculus and differential equations, and gotten the significance of the sign change without a hiccup.