I would go with invisibility. Time travel can mess stuff up.
EDIT: I'm glad this is back. Many memories in this thread.
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Time travel while the past is interesting in many ways I'm more interested in humanities future how far do we get? What changes are made (politics,religion,science,human rights and so on) and though I'd be locked up as a nut if things have gone to crap (zombie apocalypse,WW3,ethnic cleansing etc etc) then I could warn ppl when I return with proof. (Would probably end up having my time machine taken off of me by the military/gov)