The design firm uses the number "4" as a symbol for their business approach, which is to design with solidarity, calm, stability, and a "sense of home" in mind. The client wants their clients to get a sense of calm when they hire Number 4 Designs. The "4" is also inspired by the facts that there are 4 walls in a home, 4 seasons in a year, 4 elements, and four directions-- all of these things influence interior design with their colors and other characteristics.
The client's concept influenced the logo design and the final logo was able to combine all of the previously mentioned concepts into one, simple logo and brand identity.
The design firm also occasionally uses the number "4" solely on marketing materials to further the power of the number, even if it is not accompanied by the words, "number" and "designs".