My 2 old horses both had personal freezemarks I had "M0L" for Mollie and "SCOT" for Scottie, if you have them done by Freezemark instead of Farmkey you can have up to 5 letters, so if its available you can have CHAD
I had mine done by Freezemark two years ago. I chose them over Farmkey as Farmkey said the freezemark must contain a number, but Freezemark offered the option of having only letters. Don't know if this is still the case though... My pony's nickname is 'Foo' and that is exactly what his freezemark is. He is grey, so they would only do him on his shoulder, and I thought if it's something I'm gonna see all the time, I want it to be something I like!
freezemark are good - my horse is called kerry but i call her kezi and thats what i had from freezemark - ring them tell them your horses name and they will see what they got available and come up with suggestions if the one you want has gone.