Power supply for multiple parallel LED strings?
Get a single 6V wallwart and assume each letter is drawing 140-180 mA of current, so you find one that can source enough current for 9 letters. Put a 5W resistor that can drop 6V down to ~3 V and give you ~1.6A (a real big 2 ohm should work for that, or even better a couple of 5W 5ohms in parallel), noting that you're gonna dissipate a full 5W in that resistor) in front of the whole thing.  If relying on one big current regulation resistor bugs you because the not perfectly matched parallel loads will vary a bit in brightness, tailor your resistor size to the number of LEDs, noting that each LED wants up to 20mA. Same principle.