Well, they’re named after Clan McDonald.
Also, in the movie “Time After Time”, Malcolm McDowell’s character referred to McDonald’s as “that Scottish place”.
Fitting for this thread, the chain was actually named for its McDonald brother founders, who were the American sons of Irish immigrants:
https://en.wikipedia.org/wiki/Richard_and_Maurice_McDonald
(I believe “McDonald” is the Irish spelling and “MacDonald” would be the Scottish spelling.)