Voice actors play a minor role in a video game anyway... I don't see a strong connection or that they identify with these games.
I prefer signatures of the game creators/developers... and most of them are happy to sign their games for free.
Got many of my LucasArts-adventures signed by Ron Gilbert, most of my Broken-Sword-games by Charles Cecil, The Longest Journey & Dreamfall signed by Ragnar Tornquist and so on.
The only voice actors I'd love to sign my games are David Hayter and Jennifer Hale.