They definitely don't check the signature. About a year ago, I altered the way I sign cheques. I used to sign my full name, now I just initials them. I got not problem, no cheque bounced.
A few years ago, I was going through the process of changing my name. I was endorsing checks with my new name and depositing them into accounts with my old name -- a completely different name, and still no problems! I imagine this happens fairly often with newly-wed women.
Also, the signature on my current driver's license is a squiggly line.
This may be mostly true, or even universally true now, but it hasn't always been. I remember trying to make some major modification on an account with a local bank in Chicago around 2000 --maybe closing it?-- and the bank officer with whom I dealt actually brought out a physical record of my signature to compare against what I was currently signing. (Since I'd opened the account some years ago, it took me a long time to guess how I'd signed back then and to reproduce it successfully. For some reason, the officer was perfectly willing to let me try until I satisfied her, but not to accept that I was who my ID said I was.)
The ATM then tried to return the check to me, but there was some kind of paper feed error and I never saw it again.