"It seems to be a key for the sickroom. Its tag says "402"."
The Sickroom Key (病室のカギ Byōshitsu no kagi ) is a key item featured in Resident Evil 3: Nemesis.
This key unlocks the door to Room 402 in the 4F passage. Initially, this closed door reads: "It's closed. The sign reads, "402".". The key can be discarded by Carlos after opening the sickroom. He will be asked about it on the system message.
The Sickroom Key can be found in the Data room. It doesn't changes it's name after checking the item.