Question: My brother just left for a trip to Nepal for several weeks of trekking. Before he left, he was close to signing a lease on new space for his business. Apparently, the landlord didn't get the lease agreement to my brother before he left, even though all the terms had been agreed to. So he called me from the airport to ask me to sign the lease for him when it comes to his office. Can I legally sign the lease for him or will I be committing forgery?
Under the law, a person commits forgery when she alters a legally significant document in a manner intended to defraud another person. A legally significant document is one that affects legal rights or duties, a definition that certainly includes the lease in question. In the situation you describe, you have been asked to sign for someone else and would be doing so only to assist that person. You are not intending to defraud anyone nor are you doing so. Thus, you would not be committing fraud by signing the lease on behalf of your brother.
Be aware, however, that there is a particular way that this signing should be done to make clear that you are signing with your brother's express authority.
When one person gives another permission to sign a legally significant document on his behalf, the signer is essentially acting as an authorized representative for the other person. When your brother asked you to sign the lease on his behalf, he was, in effect, appointing you as his agent for that limited purpose. Under the law, this is called "procuration," which means by proxy or agent (basically, one acting on behalf of another with the other's authority).
Signing as a proxy or agent is limited to a specific purpose, like signing your lease. Where a person is appointed to act as another's agent for all legal purposes (as opposed to the single, limited act that you have been appointed to perform), this is called "power of attorney." A person with power of attorney for another may sign all legally significant documents on behalf of the other person.
Your role, as mentioned, is confined to the single act that your brother authorized you to perform: signing the lease on his behalf. That act is the scope of the authority that your brother expressly conferred upon you. This means that you cannot sign other documents on his behalf based on his permission to sign just the lease.
In order to legally sign for someone else, the signer must have the express permission of the person she is signing for. For example, if your brother had not given you explicit permission to sign the lease, but you believed he would have so you signed to help him out, you might be in trouble.
Although it's clear to you and your brother that he gave you explicit oral permission to sign this lease, the landlord may require that this permission be put in writing. In fact, any cautious landlord would do so. The last thing a landlord wants is a lease signed by someone who purports to be an agent of the tenant but, in fact, is not. So although you have permission from your brother and would not be committing forgery, you might run up against a cautious landlord who will insist on written proof of this permission (and don't be surprised if the landlord requires the document to be notarized, too). In short, that phone call from the airport might not do the trick.
If the landlord takes your word for it and allows you to sign for your brother, be sure to sign in a way that indicates that you know you're signing on his behalf. The letters "p.p." before your signature on behalf of your brother indicate that the signature is under procuration (that is, on behalf of another with permission). You may type or handwrite the letters just to the left of your signature to indicate that you are signing under procuration. Your brother's name should be printed or typed under the signature line.
If you're still worried about the signing and want to make sure you sign it in the right way as your brother's agent, or the landlord insists on written proof that you have this permission, talk to a lawyer with experience with powers of attorney, such as an attorney who handles estate planning.