The phrase "yellow sticker" usually refers to a label or tag placed on a product in a store that shows a reduced price or special offer. Full definition
When shopping for new appliances pay attention to the big yellow stickers. (moneysense.ca)
My son noticed that one of the many bright yellow stickers on the AMG G63 warned, «Do not load items on the roof. (bestride.com)
Large yellow stickers featuring the official shield of the city of Stockholm grace garbage cans proclaim: «Here is the closest garbage can!» (treehugger.com)