I'm not sure if this is still the SAE 30 oil. Does the "HD" stand for "Heavy Duty" or High Detergent? Thank you!
HD stands for High Detergent. At least in the “normal” rating of oils.
Usually used for diesel engines to help keep them clean.
Not a good idea to use in gas engines as it can clean the bores of old grime and then they start to smoke.
But since it does say in small print on the label it is for gasoline engines, then it may well just be “marketing BS” to get people to think it is better than the product next to it on the shelf.
One way to be sure is to check the detailed classification on the back of the can, that will, or should, give the detail.