Source: Wikipedia, "Quantum (video game)", available under the CC-BY-SA License.
The premise of the game was related loosely to quantum physics in that the player directed a probe with a trackball to completely circle atomic "particles" for points, without touching various other particles. Once the particles were surrounded by the probes' tail they were destroyed.
Entering one's initials for the game's high score table was unique compared to all other games of the era; the player would use the trackball to circle the letters of his or her initials in the same fashion that was used to circle the particles during gameplay. If the player achieved the highest score on the table, the initials screen was preceded by another in which the player would use the trackball to actually draw his or her initials in an entry box. Some players were adept enough with the trackball to actually write their names legibly in the box.