When you evaluate safflower/sunflower in the store, it may not be clearly labeled HO vs non-HO. The HO version is sometimes labeled "high temperature".
Regardless of the labeling, you can tell by looking at the nutrition label. Compare the % of monounsaturated fats and the % of polyunsaturated fats. In an HO oil, the mono fats will be much higher than the poly fats. In a non-HO oil, the poly fats will be much higher than mono.
In my HO safflower, I think it is roughly a 3:1 ratio of mono vs poly -- 75% or more monounsaturated. In the non-HO safflower, the ratio is reversed.
To further confuse the issue, there is a "mid oleic" version of sunflower. Not sure if there is a mid-oleic safflower. If I remember correctly, I believe Carolyn (cmhaza) uses mid- or high-oleic depending on price and says both types work fine.