I made a re-usable LED protest sign. This sign is powered by an Adafruit M0 Adalogger. A text file with messages is stored on the LED card, and messages scroll across the LED matrix. The holder uses a dipswitch to select the message from the text file.
I brought this sign to the March for Science in Washington, DC, on April 22, 2017. Although it was raining, a clear plastic trashbag protected it from the elements, and it survived the march.