Das computermachine ist nicht fuer gefingerpoken und mittengrabben!

Unlike the compact and commonplace electronic devices of today, early computers were banks of electromechanical equipment that might comprise an entire room, whose workings remained mysterious to the average person. Instead of a television-like monitor for displaying output, the state of various processes might be indicated by paper printouts or by banks of lights. Because the machinery was complex and sometimes delicate or even dangerous, only specially qualified personnel would be authorized to operate it.

People involved in computing and other scientific or technological pursuits are known to have a sly sense of humor. So when they post a sign to keep people away from sensitive equipment, it is likely to read more amusingly than "Do Not Touch". One popular type of sign for this purpose was an official-looking notice, written in mock German, warning casual observers to keep their hands away lest something break or otherwise go wrong, and advising them instead to sit back and watch the lights blink. The actual text of these signs varied, but a typical sign, such as this one from the Jargon File, would read something like:

ACHTUNG! ALLES LOOKENSPEEPERS!

Alles touristen und non-technischen looken peepers!
Das computermachine ist nicht fuer gefingerpoken und mittengrabben.
Ist easy schnappen der springenwerk, blowenfusen und poppencorken
mit spitzensparken. Ist nicht fuer gewerken bei das dumpkopfen.
Das rubbernecken sichtseeren keepen das cotten-pickenen hans in das
pockets muss; relaxen und watchen das blinkenlichten.

According to the Jargon File, such signs may have been inspired by similar mock-German signs posted in Allied machine shops during and after World War II.

Blinking lights are generally impractical as indicators in modern computing, although rows or grids of lights still do exist for use in special applications. Some of these displays have been dubbed "blinkenlights" as a nostalgic tribute to computer engineering history, and as a continuation of its quirky humor.