These days, I suppose we could add the Unicode character for := ≔ U+2254 COLON EQUALS and there is also ⩵ U+2A75 TWO CONSECUTIVE EQUALS SIGNS if

These days, I suppose we could add the Unicode character for := ≔ U+2254 COLON EQUALS and there is also ⩵ U+2A75 TWO CONSECUTIVE EQUALS SIGNS if you find typing two = characters fatiguing...