Partially true. The reading goes like this for a E10016-D2. E is for electrode, 100 is for minimum tensile strength in KPSI. The second (1) is for welding position, and the (16) is for polarity and special notes. While the (D2) indicates alloying elements.
When it comes to positions the numbers go:
1) All positions
2) Flat welding and horizontal fillet welds
3) Flat only
4) Flat, horizontal, overhead, or vertical down.