Just noticed it yesterday while putting more in air in them . It's 4E in a circle . Rolling resistance rating ? ( 4 = Level ( 1 > 4 ) , E = Energy ) ? No mention at Continental under reading a sidewall . Does get an 10 for Fuel Efficiency .
Tires for European markets come with a rolling resistance/fuel efficiency rating label, but I don't think this information is actually imprinted on the sidewall. Or has US started some new LRR labeling recently?
What exactly does it say? You mentioned "4E" but the photo you posted shows "E4".
According to Continental:
Continental tires are marked in accordance with international regulations. So the sidewall of tires intended for use in Europe are marked with a circle containing an E and the number of the country of homologation.This marking is followed by a multi-digit homologation number, e. g. E4 or e4 (4 = Netherlands)