Image source
Granite door-jamb of Kha-sekhemui. Dyn. II.-
"This great block of grey granite is the oldest piece of inscribed building-stone known. It was left on the site, pending its removal to the Cairo Museum. The repetitions of the Horus-and-Set name of the king are in the same taste as the repetitions of the Horus name in the step-pyramid of Saqqara. The inscription is identical with that on the objects found in this king's tomb at Abydos."
From _Hierakonpolis_, Part 1, by J. E. Quibell, B.A., With Notes by W. M. F. P.

TeVelde explains further:

"The Horus name of a successor of Peribsen is Khasekhem (the power has appeared). It has been suggested that Khasekhem is identical with Khasekhemui (the two powers have appeared). If that is indeed the case, 2) then we should have a development reminiscent of Sekhemib taking the Seth name Peribsen. Over the serekh in which Khasekhemui is written, however, the Seth-animal does not appear alone, but in company with the Horus falcon. The name Khasekhemui is sometimes supplemented htp nbwy imyw.f (the two lords who are in him, are reconciled). Thus both Peribsen's Seth name and Khasekhemui's Horus-Seth name proclaim the reconciliation of Horus and Seth."

_Encyclopedia of the Egyptian Pharaohs_ by Darrell Baker gives the hieroglyphs (page 177), which I referred to when creating the serekh

Here is that door jamb in its entirety:

From _Hierakonpolis_, Part 1, by J. E. Quibell, B.A., With Notes by W. M. F. P.

There is more evidence of Khasekhemy's name in granite, however this evidence is in fragments. Nekhen News, Volume 11, 1999 of tells about them, discovered in 1935. However, they weren't published back then, possibly because it's impossible to reconstruct the whole object. Fortunately, enough pieces can be assembled to show his name:

"Probably the most important of our fragments measures a mere 27x22cm. It bears the name of Khasekhemwy, “The Two Lords are at peace with him.” The name is inscribed in the frame of the royal serekh, a formalized element of palace architecture surmounted by a Horus falcon and the Seth animal facing each other, a motif unique to this king."

Furthermore, Petrie in _Royal Tombs II_ shows Khasekhemwy's seal impressions that were found in Umm el-Qaab, tomb V. Fortunately, this book has been scanned by Google, as before we could only depend on the image capture made by "FRAF":

What is going on with seals 197 and 198? The image representing Set is undergoing changes. Sometimes it is as the traditional Set animal, and sometimes it is different. Could it be in the second Dynasty, they hadn't quite decided on its exact representation?

With a closer look, two of the Set and Horus combinations are wearing the double crown (Pschent) combining both the crowns of Upper and Lower Egypt.

Neither Set nor Horus are wearing crowns in seal 200

Meanwhile, here are some photos of Khasekhemwy's seal impressions:

Period - Dynasty 2 (2686BCE-2890BCE)
Found at - Abydos, height 5 cms length 8 cms width cms diameter cms
Petrie Museum UC36854

"Description - Yellow mud sealing fragment with parts of two impressions of cylinder seal: serekhs of Khasekhemwy surmounted by Horus (falcon) and Seth both wearing double crowns with tiles: wd3 hrw pr hri wdb and hri hrwt pr hri wdb "two lords (double falcons on stand".

Period - Dynasty 2 (2686BCE-2890BCE)
Measurements - height 2.9 cms length 2.1 cms width cms diameter cms
Petrie Museum UC30392
"Description - Clay sealing, single specimen, incomplete. Top of Serekh is surmounted by the Hawk and the Seth animal, showing it is the Horus-Seth name of Kha- Sekhemui, 9th King of Dyn II. The sign h' is visible as the top sign in the serekh."