How can you tell a ladies bike and mens bike?

With motorcycles there is no such thing! I ride big bikes! If you mean a push bike the frame bar is parralel to the street on an mans bike and high up. If you were wearing a skirt you would be indecent! A womans bike has two bars running from the peadles to the front axle, much lower down than the mans bike. In reality this is a little old fasioned as women don't ride bikes in skirts much these days so many women choose mens bikes.