It is well known that a visitor is more likely to complete an activity if there is payoff at the end.
Chaner’s Computer Place has a small robot (a modified Roomba) that can be programmed via GUI to move about in particulars ways. On top of the Roomba is a horseshoe magnet. If the robot is successfully maneuvered so that the magnet arrives at a particular target, it activates the Robot Park sign so that it whirls and flashes.
I set out to build the sign entirely from scrapped and scavenged parts. The timers were taken from a defunct exhibit that had been discarded; the mechanical parts were taken from the scrap bin; the motor that drives the “P” and “R” is from an old VCR; and the gray wheels are from a Lego set. The only items purchased were the letters themselves.