can i mention public agencies?

am i allowed to mention public companies?

like i ate at Mcdonalds

or

I wrote a letter to The U.S. Department of Commerce

Public agencies

Yes. You can not only mention them, you can say things like "I ate at McDonalds and I thought the meal was overpriced." So long as you are not writing something you know is untrue you're are fine. You can't write "I ate at McDonalds and found a mouse tail in my Big Mac" unless it is the truth.