You will make a sketch that will retrieve a string from a web API and display it on DMD.
Check API every 60 seconds for update and display data.
On check, if data exists, pulse D2 3 times (I have beeper here) to attract attention to DMD.
Scroll the text
after 1 minute, check again.
Please let me know what the API is, so that I can try build you the code. Do you already have the DMD and ethernet shield?