I'm working on a an ad for my company. The company name, when typed out, is in all caps. I work for a law firm, so the company name is three last names. I am currently typing it out as follows (using fake names here):

**SMITH, JOHNSON & BROWN, PLC.**

I was just told by the previous graphic designer, who is now the head of IT, that when using all caps I should not put a comma after **SMITH**. I've been a graphic designer for nearly 14 years and I've never heard of this rule before. It seems to me that if I did not put a comma after **SMITH** it would make it seem like **SMITH JOHNSON** is one person. 

Am I correct in my thinking? What is the correct way to punctuate this?