Full color display works amazing for words and simple graphics without any SD card storage needed. This is an easy project. Just connect the wires and upload the code!

Full Color Display: $8 - https://www.pjrc.com/store/display_ili9341.html
Teensy uController: $20 - https://www.pjrc.com/store/teensy31.html
Any battery pack: $10 - https://www.sparkfun.com/products/339

double_darn cycling hat: http://www.doubledarn.com
transistor for brightness control (not totally necessary): https://www.sparkfun.com/products/521

Background....
I used this for a music festival (Pickathon in Portland, OR) to show which bands where playing on which stages....

Step 1: Solder It and Program It

The connection details are on PJRC's site:

https://www.pjrc.com/store/display_ili9341.html

connect power to both teensy VIN and Display VCC ( 3.6 to 5.5 volts)
connect ground to ground
connect display pin CS to teensy pin 10
connect display pin reset to teensy pin 3.3v
connect display pin D/C to teensy pin 9
connect display pin SDI to teensy pin 11
connect display pin SCK to teensy pin 13
connect display pin SDO to teensy pin 12
connect display pin LED to power via 100 ohm resistor (or use a transistor describes below)

It instructs you to put a 100 ohm resistor inline between the 3.7v and LED backlight.

I also put a transistor and output a PWM so that I could vary the brightness and power of the backlight. This is not necessary but full power the LED backlight drew ~100ma and the teensy microcontroller used around 40ma....so by sending a PWM signal and turning the LED down (as it only has to be 1/2 brightness at night) you can reduce the total power to ~80ma for everything (controller and display) which equals longer battery life. Here are two transistor tutorials:
1) https://learn.adafruit.com/adafruit-arduino-lesson...
2) https://learn.sparkfun.com/tutorials/transistors

I didn't have a proper battery connection for the battery so I used another uController I had laying around (the gemma)...It is the small round thing the battery plugged into in the picture. Here is a proper connector: https://www.sparkfun.com/products/9749

I used a 2000 ma power supply and it never went out after 8 hours of constant ON time.

You could also use the Teensy micro usb connector and plug the thing right into a small backup USB power supply: http://www.amazon.com/s/ref=nb_sb_noss_2?url=searc...

The arduino library has an example graphics test that you can build your sign from:

https://github.com/PaulStoffregen/ILI9341_t3

Go to the download as ZIP button and put the library in your Arduino Libraries folder, restart Arduino, and open the example graphics sketch.

Step 2: Going Further...

You can add more graphics and video by using and SD card to store the data.

You could also put an excelerometer on the hat so you could display graphics based on your motion. You could add a microphone and do a simple equalizer to the color display. You could add a real-time clock and do real-time schedule updates. This is fairly easy to do on the teensy.