Com or ask your property manager about Leap. Cosigners sign the apartment lease with you, taking on the same financial responsibility as a tenant and then some.We take care of the screening and stand behind renters we approve. Over 90 Properties to choose from! A guarantor or cosigner for an apartment could help you fill financial gaps when applying for your rental. Find which is right for you. Signer is a trustworthy individual who serves as a voluntary guarantor. Like any other contract, a lease cannot be changed in the middle of the lease term unless both parties agree. A cosigner is a person who signs your apartment lease and shares responsibility for rental payments. The cosigner agrees to pay your rent if you can't.