cleanskin

Short definition from Wiktionary

Noun

1. 1
   An unbranded animal.
2. 2
   A person who does not have any tattoos.
3. 3
   Someone with no prior criminal record, a person with no previous convictions; loosely, someone who has not done anything wrong before, an unblemished character.
4. 4
   An unlabelled bottle of wine.
5. 5
   An undercover police officer who has not done a particular task before.
6. 6
   A cricket bat with no maker's logo