Here is a flexible LED matrix you can use with the Arduino Mega, Raspberry Pi, and other platforms to display messages. This 4×32 Flexible RGB LED Matrix has 2048 LEDs, 2 IDC connectors, and 12 16-bit latches. According to Adafruit, these displays are chainable.
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These panels require 13 digital pins and a 5V supply. More information is available here.
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