If Paul McCartney is looking for his birth certificate, he should check in Houston, where it is expected to go for $20,000 in a weekend auction. The document is being put on the block by a Houston woman who says she got it from someone who bought it from McCartney's stepmother. "We did research on the handwriting, the paper, the stamps, the writing, the deputy register's name and his writing," said Ray Simpson of Simpson's Auction Galleries. "It is unconditionally guaranteed for its authenticity." The owner says she unsuccessfully tried to contact McCartney to see if he wanted the document back. "If Paul McCartney asked to have it returned, nothing would please us more than to have this document returned to him," Simpson said. The certificate documents the birth of one James Paul McCartney on June 18, 1942, in Liverpool, England, and lists his parents as James McCartney, a "centre lathe turner" at an aircraft factory, and Mary Patricia McCartney.