need the person only hand the document to him, or is a signature from him required?
As I understand the statute, the defendant's signature is only required on the Post Office return receipt form, and only if you serve him by certified mail with return receipt requested. For in-person service, the process server only needs to be successful in giving him the documents, and must then file with the court an affidavit of service signed by the process server (not by the defendant).
If verbal identification and handing the document over is all that is required....it makes me think of a means he could be coalesced into presenting himself :)
I'd guess it's up to the process server what evidence of the defendant's identity they consider sufficient so they feel comfortable signing the affidavit, in which they promise the court that they have succeeded in serving the correct person.
BTW, RCW 4.28.080(17) doesn't require personal service on the defendant or a signed return receipt. Instead, as I understand it, your process server (or a friend willing to sign an affidavit of service and take the risk of possibly having to show up in court) could arrange to meet the property manager of the defendant's apartment complex at the doorstep of his unit and give that person the documents, after which you'd have to mail the documents to him as well, but only by first class mail.