The Queen Mary harp has three sets of markings on it which could be considered inscriptions.
There are small paper labels stuck to the front of the soundbox, with letters on them, to label certain of the strings. I presume these may date from the early 19th century when the harp was strung in gut and played by Elois, but they could perhaps be older, dating from when the harp was played in the 18th century. They are upside-down, to be read by the (left-oriented) player of the harp, and appear to be cut from a printed sheet, rather than handwritten. The letters and position numbers are as follows, counting from the treble: 1 [illegible], 8 [c], 9 [b], 11 [G], 15 [C], 22 [C]. These letters match the gamut described by Gunn as being settled on through trial and error.1
The side of each fish head has carved designs that have been interpreted as the letters DO, perhaps meaning "Deo Oblata" (offered to God)2. However they could also be interpreted as 3-part geometric designs, as there are three fields; the middle is like the letter O; the outer end is like the letter D, and the inner end is wedge shaped to follow the eyebrow of the fish but otherwise is a mirror image of the outer end. There is a vertical braided strip between the three fields as well.
The tuning pins bear hidden scores that have been interpreted as ogam letters3. The scores are only visible when the pins are removed from the harp; Patton3 prints a NMS photograph of the pins laid out on a table. One pin has 6 scores; the remainder between none and five. No stemline seems to be indicated. The visible ends of the pins also bear incised lines and decoration in the form of concentric bands and crosses or cross-hatching. Comparing museum photographs from the early and mid 20th century shows that not only have some pins been lost, but some of the remaining ones have been moved between holes, so the original order of the pins cannot be preserved.