Does a DC toy motor emit AC when you spin it?
I would be surprised if a cheap DC toy motor contained a rectifier
  diode since it's designed to be a DC motor, not a DC generator


A cheap DC motor of the type that has a permanent magnet stator uses brushes and a rotor commutator to continually reverse the current into the rotor coil thus the effect is like feeding AC into the coil: -



If you didn't do this the rotor would spin maybe up to half a full turn and stop. Then it would take too much current and maybe burn out.

When driven as a generator the commutator does indeed work as a rectifier to produce a DC output: -



Maybe you are thinking that a cheap motor uses slip rings. This type of motor requires AC and will produce AC: -