There is not much known about Strong's Coffee, as all that is shown is a billboard. The billboard depicts a man (bald, presumably aged 40-55), drinking a cup of coffee. This man shown on the billboard most likely is the mascot. Either that, or he was hired to promote the company on a billboard.
Mermaid Man and Barnacle Boy are riding on top of a crystal with wings, until the crystal clips the top of a billboard. That billboard was for a business known as Strong's Coffee.