M.D.A.I.K. 52 pl. 14d.
Engel, Das Grab des Qa'a..., 440, fig. 217.4
(The drawing is in T.A.H.Wilkinson,
'Early Dynastic Egypt', 1999, p.79)
Semerhet 3
Abydos, Umm el Qaab Q (Qa'a)

G. Dreyer seems not to have noted the name of Qa'a on the upper-right portion of the label.
It's not a small serekh, rather a compound which probably refers to the harim of (prince) Qa'a.
This might be of some importance in relation to the supposed difficult succession Semerkhet/Qaa (based on the questionable interpretation of "usurpations" of inscribed stone vessels).