The problem is that powers of attorney do not have to be filed, so there may be none on file; furthermore, as a general rule, people relying on a POA to deal with the attorney-in-fact (the person given authority by the POA) do not need to verify it with any official source, like the county clerk: if it looks valid, they may act in reliance on it. So there is not necessarily any more way to check that a POA has been forged for you than there is to check whether a contract was forged with your signature.