Digital signs are unfairly perceived to be hazards to driving.
The perception is that they distract drivers by making them look away from the road. The premise is sound, but not accurate. Most of your audience, especially if they are the person behind the wheel, will only give your sign a few seconds of attention at most while passing by.
In those precious few seconds, they are not going to remember your phone number.
Let alone have time to grab a pencil and write it down. Google or Siri will help them find your phone number if they want to reach you. Use your advertising time with better content and better call to action.
You need them to remember you, not a phone number. Don’t waste your precious resources on this ineffective marketing practice.