A few giveaways of a cleaned coin is a harsh, shiny coin with flat luster. Multiple hairlines around the fields also usually signify harsh cleaning. If the amount of wear on a coin doesn't match its color, then it's probably cleaned (for example: who's ever seen an AG-03 Red 1909 Lincoln Cent?) Hope that helped!
Just like there are thousand different ways that a coin can be harshly cleaned, there are a thousand different indicators that a coin has been harshly cleaned. Problem is, those indicators can have entirely different meanings. In other words, on this coin they may indicate that it has has been harshly cleaned. But on that coin they may indicate that it has not been harshly cleaned. As a collector what you have to do is learn to distinguish between the nuances of these indicators. And the best way to do that is by experience - one coin at a time. I'm guess what I am trying to tell you is that a simple listing of a few possible indicators can be more harmful for you than it can do you good. That is because the same thing can mean different things with different examples. The best thing to do is to post pictures of specific coins and then talk and discuss those specific coins and what the indicators on that specific coin mean.
