If a guarantor is required, Guarantor must complete and sign the Lease Contract Guaranty. Each Rent Guarantor must complete a Rent Guarantor Application, sign a Guarantor Acknowledgement, and sign and have notarized a Guaranty of Lease Agreement.A guarantor is a person or a company who will co-sign on your lease in case you do not qualify to rent an apartment in New York on your own. This guide is to offer some helpful advice and tips to ensure that your experience is a smooth and hassle free as possible. The submission of an application is not a guarantee of an apartment. • Only original applications will be accepted. Please fill out the application completely and submit the required documentation and certified funds. Signing as a guarantor for an apartment lease can definitely come with risks, especially to your credit score if the tenant defaults on rent.