The S.T.A.R.S. Card can be used on the computer in the Raccoon City Police Station's Main hall to watch the password, that locks the locker box, that contains the S.T.A.R.S. Key in the Evidence Room. Checking this computer without having the keycard, a message can be read: "This terminal controls the security system. I could operate it if I had a S.T.A.R.S. Card.".
Brad's S.T.A.R.S. Card can be obtained from a Card Case found when you examine his body after his death. However, if you choose to escape into the Police Station rather than fight the Nemesis-T Type, you will have to search for Jill's S.T.A.R.S. Card, which is located in the Meeting Room.
Either card will not disappear from your inventory after use and cannot be discarded.