P-plate

noun2

1. •
   (UK, Australia) A plastic square sticker or sign bearing a large letter P, placed on a vehicle to indicate that the driver only has a probationary driver's licence, for various possible reasons.
2. •
   (UK) A plastic square sticker or sign bearing a large green letter P - optional not mandatory - placed on a vehicle, probably to indicate that the driver has recently passed his or her driving test.