It is unlawful for any person to engage in, or carry on, or to represent and
advertise himself as engaged in or carrying on the business of plumbing
contractor, or sewer contractor in the City of Portland, or to use the words
“plumbing contractor,” “sewer contractor,” or “plumber,” or “plumbing,” or
expose a sign containing similar import for such purpose, implying that the
advertiser is so engaged, unless such person has obtained a registration to
engage in and carry on a business of plumbing contractor or sewer contractor in
the City of Portland.