There is a pair of letters at the very front of every Windows program that most people who run those programs will never see. Open any .exe by its first bytes and you find them waiting: MZ. Like the PK that heads a zip archive, these are initials, and they belong to a person. MZ stands for Mark Zbikowski, the Microsoft architect who designed the executable format in the first place. He built the structure that lets the operating system recognise and load a program, and he signed the front of it with his own name.

The reach of that small mark is what makes it worth an exhibit. This is not a signature on a single rare file. Every Windows executable since the days of MS-DOS has opened with those two letters, an unbroken lineage running from the earliest personal computers to the software running on machines today. Decades of programs, from ancient utilities to the latest applications, all begin identically, all carry the same architect's initials at their head. When you double-click almost anything on a Windows computer, you set in motion a file that starts, quite literally, with Mark Zbikowski's name.

The exhibit's sniffer makes the hidden thing visible. Reading a file locally by its opening bytes, without sending it anywhere, it shows you the signature sitting at the front of your programs. Feed it any executable and there is MZ, before a single line of the software's own work. There is something moving in the durability of it. Formats are usually thought of as impersonal, cold arrangements of bytes agreed on by committees, and yet here, at the head of one of the most-used formats in the world, is a human being's monogram, preserved by sheer continuity for the better part of half a century. The signature outlives the era that made it. Every time a Windows program starts, it quietly re-announces the name of the person who decided how programs would start.