Currently there are two kinds of yellow flags - those you can overtake under and those you can't. Unfortunately in the heat of battle or while desperately trying to avoid the pile-up ahead it's near impossible to read/digest the caution flag's accompanying text. So how about a caution flag specifically for non-overtaking situations? Something like this?
The idea is good, however such a flag does not exist in reality and would cause a lot of confusion. Maybe it would be a better idea to tweak the existing logic and adapt it to real world usage - isn't overtaking always forbidden under yellow flags? Or use single and double yellows, also as in reality.
Single and Double yellow flag only influence the Speed that you're allowed to drive. Overtaking is allways forbidden. How should anybody know if it's allowed or not.