Because a Notary is required to change the Deed during a For Sale by Owner sale, the timing of signing can get a bit tricky.
A Seller can sign the Deed in the presence of a Notary at any time that is convenient after it certain the property sale will close. But the Seller should only present the signed and notarized Deed to the Purchaser (or the escrow agent) at or near the time of the Closing.
More common is to not sign the Deed in advance of Closing. Rather, the Deed is usually signed and notarized at the time of the Closing, when the Seller receives the purchase amount for the property from the Buyer, usually by certified check or wired funds. In essence, that payment is exchanged for the Deed.
Signing the deed prior to receipt of the purchase price presents some risk, as the signed and notarized Deed could be filed (if it leaves the Seller’s control or possession), thereby permitting the title to transfer to the Purchaser before the Seller receives payment for the property.