An indorsement may be in blank or special. An indorsement in blank includes an indorsement to bearer. A special indorsement specifies to whom a security is to be transferred or who has power to transfer it. A holder may convert a blank indorsement to a special indorsement. An indorsement purporting to be only of part of a security certificate representing units intended by the issuer to be separately transferable is effective to the extent of the indorsement. An indorsement, whether special or in blank, does not constitute a transfer until delivery of the certificate on which it appears or, if the indorsement is on a separate document, until delivery of both the document and the certificate. If a security certificate in registered form has been delivered to a purchaser without a necessary indorsement, the purchaser may become a protected purchaser only when the indorsement is supplied. However, against a transferor, a transfer is complete upon delivery and the purchaser has a specifically enforceable right to have any necessary indorsement supplied. An indorsement of a security certificate in bearer form may give notice of an adverse claim to the certificate, but it does not otherwise affect a right to registration that the holder possesses. Unless otherwise agreed, a person making an indorsement assumes only the obligations provided in § 8-108 of this title and not an obligation that the security will be honored by the issuer.