Contract with one signature can/will be enforceable if the other unsigned party wants to. One contract/agreement that has signature lines for both parties and one party signed it but other party hasn't signed yet means the signed party has agreed the contract and waiting for the agreement from the party. This agreement is in a "pending" state, but definitely not "voided". The signed party never able to argue this contract is voided.
The other party has not signed the contract will have many options. She can argue she never agreed the contract if she wants to break the contract before the end of the term or not follow the restriction sets in the term. The signed party will never able to bring a contract with one signature and ask enforement. The sentence "One signature is not a contract" will be 100% true in this situation. The unsigned party also has another option if she wants to enfore the contract by signing it. Becasue the contract is in pending state, if no law defines the signing expiration time, it generally only expires by the end of the term sets in the contract. She can sign anytime before the end of the term.
Once you signed the contract, you closed the window from arguing the term in the contract and give the steering wheel to other party. Which way the other party will drive, you will have no more control.
The conclusion is - in the tenant/landlord battle, a contract with only landlord's signature will be deadly for landlord in either the tenant wants to break the contract or the landlord wants to enfore the contract.
