system
Given the following post, respond as if you're commenting on Reddit:
human
[General] What's a biological tell-tale sign that someone is a time traveler ?

Is there a way to tell that a person is a time traveler thanks to some kind of medical test/examination ? Like a blood test or something more on a par with the technology of the era. On a long scale aswell as on a shorter scale like a dude from 20something going back to the 60'.
gpt
Generally it's quite difficult to tell unless you know what you're looking for. Someone being far healthier than the standard person could be a sign of a traveller from a higher base health standard future coming back, or it could just be evidence that this person is remarkably healthy.

The tell-tale signs are definitely going to be obvious things like bionic/cybernetic implants, nanomachines, and more contemporary metal implants and supports. The latter you'd expect from say a 22nd century visitor to the modern day or prior, but even just a modern hip replacement would be considered anachronistic back in the 20th century (if the doctor happens to be poking, prodding, and potentially bisecting/dissecting said traveller).

If there's a certain biological event of massive proportions, the lack of that present in the body could also expose this person as a time-traveller. For instance, the Sole Survivor in Fallout 4 avoided the genetic effects of the nuclear radiation when the bombs dropped, highlighting them as extremely healthy to the Brotherhood of Steel but more specifically as *extremely* unique (alongside their son) for their Synth program.

You could also say that someone surviving a widespread disease like COVID-19 or Smallpox would be noticeable under the microscope, showing future observers (far enough ahead) that this traveller comes from far enough in the past to still have observable scarring/etc from these long gone diseases. Or contrasting this, potentially a future visitor shows that they've been inoculated and overcome a disease that's yet to be fully cured in that time.