If the layout is -9V it's always written as such and/or it's in the notes and in the post, at least on the main page, otherwise it's +9V. I usually write +9V its not really necessary, I just do it as a force of habit. Luckily there aren't many layouts that use -9V, and mostly appears in older circuits that use Ge trains intros before the switch to Si transistors or modern layouts that are faithful reproductions of old Ge circuits.