I don't think there's any way to do it that isn't confusing to the average owner. Every vehicle company has tried one way or another and failed. Little logos don't work. The API Starburst and Donut confuse people. SAE grading confuses people. ACEA specs aren't understood in the least. Builder approvals confuse customers. The only way that wouldn't confuse consumers is if every OEM on the planet agreed to a single specification and viscosity and back speced it to everything on the road.
Plain, simple Garak.
2008 Infiniti G37 - Shell ROTELLA T6 Multi-Vehicle 5w-30, NAPA Gold 7356
1984 F-150 4.9L - Quaker State GB 10w-30, Wix 51515