The "Shakefork" is a Y which does not go all the way to the edge of the field. I imagine there's no rule against it being inverted. Fox-Davies has this to say about the shakefork:

The pall, pairle, or shakefork is almost unknown in English heraldry, but in Scotland its constant occurrence in the arms of the Cunninghame and allied families has given it a recognized position among the the ordinaries. As usually borne by the Cunninghame family the ends are couped and pointed, but in some cases it is borne throughout.