Use our Lease CoSigner Agreement addendum to extend the legal terms of a tenant's lease to a cosigner. A cosigner is someone who signs the lease along with the main tenant of the rental property.There are times when a tenant needs a cosigner. The cosigner is a signatory to the lease, in appearance, the cosigner signs the lease as well as the renters affirming all terms of the lease. Learn the essential steps on how to add a cosigner to a lease to strengthen your rental agreement. This article gives you a complete guide to Maryland rental applications. We provide information about what a Maryland rental application should include. It is up to the landlord to consent to the amendment removing the cosigner. You may want to try offering a larger security deposit of or some other concession. However, the lease cosigner responsibilities do not end there.