Incidentally i always found the idea of an explorer grabbing the mysterious jewelled skull and getting cursed similar to the thought exercise of how we warn future cultures about the dangers of long term radioactive waste.
The warning needs to transcend language so you probably think a skull is pretty clear right? Put a big skull there, maybe make it light up or eye catching in some way just to really seal the deal? Surely they understand "don't go near this". Yet in a million years time you're probably going to get some explorer "finding the mysterious and cursed crystal skull" who will subsequently die of "the mysterious curse". It would have made a more interesting ending for that Indiana Jones movie that's for sure.