NO. Mail carriers are not allowed to sign for someone's certified mail unless it's their own certified mail.
If it's standard certified mail then anyone at the address may sign for the certified mail but if the certified mail is requesting a certain persons signature then they must sign for the certified mail.
If nobody is available to sign for the certified letter or certified mail then a slip will be left in the persons mailbox requesting them to come to the post office to sign for the certified mail.
A certified letter is sent when they want your signature to get the letter to you.
So when you send a certified letter the person will get a notice in their mailbox that they have a certified letter and that they need to sign for it.
The person then signs for the certified letter and then accepts the letter and you get a receipt showing they signed for the letter.
But the person is not required to accept the letter and may refuse to sign for the letter and not accept it.
When you send a certified letter through USPS you will have an official receipt showing proof the item was mailed and has been certified.
Then when the certified letter reaches the persons post office or postal box they will have to sign a form with their signature before they will get the certified letter.
So when you send a certified letter it is meant to prove that the person got the letter.
Very important documents and letters are sent certified and require the addressees signature to get the certified letter.
Then the person who sent the certified letter should receive confirmation that the certified letter was delivered to the addressee.
Certified letters cost more than a standard letter but it makes sure that the person gets it.
However nobody can be forced to sign for or take a certified letter so they could have it returned to you.
But most certified letters do get to the addressee just fine.