On-Prem - Modify ticket counter to use a pre-fix

For those of us who use the On-Prem installation, it would be great to be able to modify the counter to use a letter prefix.  In our situation we have 4 instances running for 4 different departments that will never cross paths.  Would be nice to be able to add a letter before the ticket so the will fail in the off chance someone replies to the wrong service account.