You repeatedly say that the sign says "2y," but the photo that you posted, as well as those from others, clearly prove that they don't make such a claim.

"¥2" would indicate a price of 2 yuan, whereas the signs say 第2个 ("the 2nd one"). Are you confusing 个 (simplified character for "piece") with ¥?

Or is your contention that the numeral "2" deceptively suggests ¥2? As with YuropFlyer's example of 9折 meaning 10% discount, this kind of advertising is endemic across Greater China. So is using 2 in the context of "2nd."

Either way, this rather bolsters the case for learning Chinese culture and language if you plan to do business with Chinese people.