I sort of remember there is a novel about someone who travel back in time and use a nuclear mushroom cloud as a signal that he is from the future.
I think to avoid drawing attention (like talking about quark, dark energy etc.) each era must have something that is iconic in the future, but people in the same era does not aware of.
Imagine someone talked about Mac OS future version and that it will run under arm. That may alert that he is from the future without too much attention.
I think to avoid drawing attention (like talking about quark, dark energy etc.) each era must have something that is iconic in the future, but people in the same era does not aware of.
Imagine someone talked about Mac OS future version and that it will run under arm. That may alert that he is from the future without too much attention.