What type of indorsement consists solely of the signature of the indorser?

A blank indorsement is characterized by the indorser's signature alone, which makes it a straightforward way to transfer ownership of a negotiable instrument, such as a check or a promissory note. When the indorsement is blank, it does not specify a particular payee; thus, it allows any holder of the instrument to claim it. This feature enhances the instrument's negotiability, enabling it to be transferred simply by delivery.

In contrast, a special indorsement includes the signature of the indorser along with an instruction specifying to whom the payment is to be made, thereby limiting the instrument's negotiability to that named party. A restrictive indorsement imposes conditions on the instrument, such as "for deposit only," which also limits how the instrument can be used. A qualified indorsement allows the indorser to disclaim any further liability, adding a layer of legal protection for the indorser but also altering the nature of the transfer.

Thus, the critical distinguishing factor for a blank indorsement is its simplicity—being solely the signature ensures maximum transferability without conditions or limitations.