You can also turn the feature lines on the propeller off. When the propeller is selected, there is a radio button on the Geom browser to turn off the feature line display for an object.
These aren't just random wireframes. One is a circle that depicts the direction of rotation of the prop. Another depicts the thrust direction. The final one depicts the rotation axis for a folding prop. These markers usually have size 1.0 -- but if your model is in large units (resulting in small numbers for dimensions), you end up with something like this -- with giant markers.
As Brandon said, set their size to 0.0 and they will vanish.
Rob