我手头上的travel certificate有这样的说明：

This certificate is not transferable and may not be sold or bartered.  However, the original recipient of this certificate may arrange travel for another person if done without selling or bartering this certificate.  Any sale or barter transaction involving this certificate, or any offer to sell or enter into such a transaction, shall render this certificate full VOID and thereupon this certificate shall no longer be redeemable by any person, including the original recipient.