I think the fine is $35 now. Its not as high as $120.
*edit#2, we were way off...
"Penalties for displaying L-plates when not a learner driver
The driver will be fined A$10. However, accredited driver trainers and rider trainers may continue to display L-plates on their vehicle after they have finished giving driver training."
*edit, the $120 is for not displaying the L plates.
" All learner licence holders must currently display an L plate on the front and rear of the vehicle
or cop a $120 fine."