After reading this post, I realized that a significant percentage of my friends and family could go to prison for forgery. Many couples I know sign one another's names all the time, including on the backs of checks. My wife and I have given one another blanket permission to sign for one another, and I know many other people with a similar understanding.
In the United States, is it in fact illegal to sign someone else's signature on the back of a check if one has permission to do so? How about signing my wife's signature on our IRS forms?