CO2 footprint would be nice, but CO2 isn't only environmental factor to consider. I'd rather have colour-coded stickers with two scales - absolute and relative within a product category.
A sticker on a diesel car would be RED/RED and a sticker on a tiny EV car would be RED/GREEN.
A sticker on an apple from a domestic market would be GREEN/GREEN and an apple imported from a country 1000s miles away would be GREEN/ORANGE.
Ideally, the labeling would be a reflection of a fiscal mechanism to charge for externalities in the entire chain - from production to a sale and disposal.
