Hi, English isn’t my mother tongue so I was asking myself that question since I first encounted a w/… Back then I was like: “What tf does ‘w slash’ stand for?” And when I found out I was like “How, why, and is it any intuitive?” But I never dared to ask that until now
Abbreviate using the first and then any choice of following letter that differentiates it from the other possibilities in a specific group: AL, AR, AK, AZ… MA, ME, MD, MI, MN, MS, MO, MT… WA, WI, WV, WY!