Toggle Preselection Highlight by selecting from the marking menu (Ctrl + Shift + right-click in the scene).
When Preselection Highlight is enabled, you can highlight components before you actually select them. As your cursor moves close to a component, a colored highlight appears on the closest component.
Preselection Highlight works on all component selection modes (Face, Vertex, UV, Edge or Multi), but only supports polygon objects.
To highlight components before selecting them
Maya automatically highlights the closest component.
When Symmetry is on and you drag your cursor across your mesh, Maya highlights the closest component and the corresponding component on the opposite side of the mesh.