A licensed contractor must display their license number on all of the following EXCEPT:

Explanation

§7030.5 requires a licensee to include the licence number in all construction contracts, in subcontracts and calls for bid, and in all forms of advertising as the registrar prescribes. That squarely covers (c) and (d), and it covers (a) as well: a business card put into a customer's hand is a form of advertising, not private correspondence. What the section reaches is the material the public sees. Internal bookkeeping is published to no one, so no licence number is required on it, which makes (b) the exception the question asks for. The purpose is the one §7027.1(a) enforces from the other side — a consumer must be able to read the number off whatever brought the contractor to the door and check it against the board's record before signing anything.