If a signature is required, Turbotax will not e-file. (However, a signature is not always required, for example with non-cash donations that do not require an appraisal.)
This is a change from prior years. In the past, Turbotax would e-file the rest of the return, print out a form 8453, and tell the customer to mail the signed original 8283 along with the signed 8453 within 3 days of e-filing. (This is one of the situations allowed on form 8453.) However for this year, Turbotax does not support e-filing at all.
