Yes, on that petcock, the short end of the arm points to the label of the position you're in. If the "On" label was at the bottom on the face plate, the long end of the arm would be the indicator.
There is a rubber disc, usually with 4 holes in it, under the face plate and arm. This is what the arm seals and turns against. It can get worn and sometimes torn up from the arm turning against it. Sometimes you can just flip it over and cure the leak. The back side is "fresh" and hasn't been subjected to the arm rotating against it. It also helps to smooth the back face of the arm, the area that turns against the rubber disc, by working it against some 400 or 600 paper on a flat surface like a piece of glass. Also check the edges of the holes in the arm plate. If they're sharp, they can tear up the rubber disc as you turn the arm. Round any sharp hole edges off with a small sharp pocket knife.
