Yup, as soon as you put anything on the outside of your trailer or truck, your commercial.
When I had a big time sponsor, they asked about lettering my trailer. I explained to them the requirements and asked for a extra 15K for the record keeping. The trailer stayed plain.
I have been employing hazmat drivers since 1984. PUCO spends 3 days here auditing my records every 3 years.
I have towed over 150K miles with my race equipment in the last 15 years and have never been hassled.
But I don't have billy bob racing down the side of my trailer either.