Washington uses signatures for our all mail in elections. When I’ve phoned in my signature (read just a line instead of something even vaguely resembling my usual mess) it has been challenged. I also forgot to sign/drop my ballot one time and had my wife sign it. That one was also challenged.

When challenged you have to reaffirm you submitted the ballot. You only “lose” your vote if you fail to respond.

YMMV but it seems to work pretty well here.