form 1040 has a signature line.

Look again.

Look closely--the new "postcard size" Form 1040 is supposed to be two half pages--front and back--but when you print it out, both sides print on one page.  Do you see the black arrow pointing to the words "Sign here" in the middle of the page?

The new 1040 is 2 half pages but now print on 1 sheet with the Signature line in the Middle.