I'm trying to create a signage schedule with a sign number that is unique to a family so I can schedule them. Is there a way to add a "Mark" to a family so that if the number is the same as another it will give you the error similar to when you have two doors with the same number... and can that number auto increment?

So when I place a sign it gives it a number 01 then I place another and it automatically numbers it as 02, if I try and change the 02 to 01 I get an error that that number is already used...

Is that possible?