Tissue samples embedded in settable, sectionable media such as paraffin can be cut into sections. Embedding one or more sectionable fiducial indicia in the medium permits identification of the plane along which the medium has been cut. However, prior methods of inserting indicia into embedded tissue sample blocks are cumbersome and difficult to perform. Sectionable fiducial indicia can be embedded in a block of medium by releasibly fixing the indicia to the sidewall or base of a mold used to shape the tissue block during embedding of a tissue sample in the medium block.