Did Salvador Dali ever sign his full signature on any of his artwork?

Yes, if by "full signature" you mean his first and last name. His full signature appears on some (not all) of his oil paintings. He also used his full signature to sign some limited edition books published in the 1940s. Keep in mind that Dali's signature varied over the years--sometimes he used "Salvador Dali", sometimes just "Dali" and at other times Gala-Dali. He also incorporated the crown symbol into his signature at times. In fact, there were so many different variations of his signature that one of his assistants (Capt. John Peter Moore) released a book showing 678 different signatures!

Also, keep in mind that many Dali lithographs/reproductions are reported to have fraudulent signatures.