Howdy,
The same thing you will propbably do with you herd. Get a bag of tags, color of your choice, design of your choice, and tag some cows. Say you picked orange tags. Say you neighbor uses yellow tags. A pretty easy identifier if they got mixed up in a field. Maybe you have some commercial and some registered.. use white tags on one kind and maybe black tags on the other.
The writing is whatever you want it to mean. It will be a means to your recoed keeping process. Year after year knowing who produces what, and what one did not produce well, and goes down the street....
I use all yellow x-large on cows, calves get the next size smaller with dams number, sire, date born. When I do tattoo later, the ear tag with be part of the tattoo. Cow 30 has calf, smaller tag 30. xxxxnamexxxx E30 I am not with the international numbering system, E=5 number in alphabet, last year had D30, next will have E30, then 2006 born would be F30 and so on.
Just do it the way you want to keep track.