No. Cookies, anonymous IPs, proxy servers, etc.; can all be manipulated. There is no way to prevent someone who isn't signed in from voting multiple times, unless you restrict voting to members only. That's an easy fix.
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Now, if you simply want to eliminate the bulk of anonymous/proxy users (it won't stop the really determined), you could do something like this. This does not set a cookie to indicate non-members have voted. That's another step.
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