Not sure sharpie will last. I used blue for 2020 and the year goes on the left leg. A secondary color goes on the right leg, to distinguish same breed apart. We named by breed...and have two RIR, two LB and two BO. The RIR's are Rosie, so I have a "red" Rosie and a "yellow" Rosie, etc.
The...
I use zip ties. The girls do not pick at or pay any attention to them...even the red zip ties are no issue.
What do you want the flag portion for? I think the flag would cause a more noticeable reaction. I leave the zip ties loose enough that they can rotate. Not sure the flag would allow...