As a tool designer, the usual practice is to use your initials in the title-block of your drawings. However, after tiring of getting chewed-out by the owner for costly, mistake-ridden designs by several designers with the same initials (including his brother), I started to use the first three letters of my last name. Maybe I was an ass for allowing him to complete his rants, but I always found it satisfying to refrain from setting him straight until after he was finished chewing me out. Tit-for-tat I suppose.