So strange it was not implemented yet. It is mandatory needed in huge amount of applications. Just add QChar field "leading character". When the digitCount is set to N and value is n length - then all leading N-n empty places without digits are filled with this character. It can be '0' with result like "0001" (digitCount=5) ot '-' with result like "–32" (digitcount=4) or else. By default it is space character with current behavior.

Internally this is just add line inside QLCDNumber:

QString("%1").arg(value, digtitCount, base, QChar(fillingChar)) ;

and add property fillingChar.