No, if a check made payable to two people, both people must sign the check. The bank should not cash a check without both signatures and if he signed your name, that is forgery. You would need to contact the IRS to get copies of both sides of the checks.
This answer is being given for general informational purposes only and is not protected by the attorney-client privilege since this is a public forum. The information provided does not create an attorney-client relationship. No communications with me on this forum shall be construed as arising out of an attorney-client relationship. If a client needs specific legal advice or opinions, he or she should retain counsel for advice or to undertake representation.
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