The first 4 letters of the code - You can only use 5 of each code per account so it makes it easier for everyone if you post the first 4 letters such as VPSG, VLFT etc. so that we know whether or not we have used our limit of this code. People are sometimes more hesitant to bid if they don't know what the code prefix is because if we used our limit then we can't use the code.
If you search VUDU credits on here you can see that most of the auctions list the prefix (first 4 letters) of the code for bidders - just so you know no one is trying to scam you or anything like that.