any sticker on cars should be alright as long as it is restricted to about 10% of the windshield, for example this would be roughly the darkened bar that is on the top ~10% of the windshield, i think you can have as big a sticker on the rear window as long as you have 2 functioning mirrors
- i came up with 10% caus this was the new law for window tinting - that the tint can cover 90% of the front windshield - which excludes the top ultra tint bar pretty much
dont take my word for it - but unless your going sticker crazy with the Auslancer / other clubs, you should be fine to put a 'large' sticker on the front, rear , sides etc without any defects being issued for it