Significant Signatures is an insert set in 2001 Donruss Classics. 83 of the cards numbered 101-200 are paralleled in this set. The stated odds were 1:18 packs or 1 per hobby box. Cards numbered 101-150 have sticker autographs while cards numbered 151-200 are hand signed. A very large number of these cards were inserted as exchange cards. Also redemptions for #162 Sandy Koufax were switched for a card of Nolan Ryan in an Astros uniform after no agreement could be reached with Koufax. Similarly Ron Santo was substituted for #185 Robin Roberts.