I screwed up a little on this one in that I forgot I should be making a forum topic before starting to populate it, but anyway...
I'd like to propose a tag for characters directly facing the viewer, or in other words a "straight-on" view. The general guidelines I've been using so far are to have the fronts of the head, torso and hips (or whichever of them are visible) all faced toward the viewer at a 0° angle, or at least very close to 0°. In this regard it is similar to the profile tag, which is for a 90° view of the head. I don't think the position or rotation of the arms and legs should be taken into account because it would mean that posts such as post #2063427 wouldn't count, even though they are clearly fit for the tag.
I started to populate it by going through the tachi-e tag, but I have yet to make the wiki. If straight-on is approved I'd like to define its guidelines here, and if it isn't then I can easily nuke it.