The flag allows the QS to filter the existing certificates list by those ready to be reviewed.
The non-QS user would select the tick box once the certificate was near completion (see image below).
Once this has been selected, the QS can then filter the list by selecting 'QS Sign Flag' in the 'Search for' drop down, then click 'Filter Certificates' to apply the search.
The search filter can also be saved so there's no need to set it up each time.
Once the QS has signed it off and finalised the certificate, the box will be automatically unticked.