This page of The Last of Us game guide contains information on where to find the artifacts and pendants in the Hotel Lobby chapter taking place in Pittsburgh. Those items are collectibles-secrets. Our walkthrough indicates the exact location of each artifact and pendant.
Artifact #39 - Note to Staff
After you make it into the hotel lobby, and walk upstairs, turn right.
Stay close to the wall and slip past the hole, where there is a suitcase with the note in it.
You will find a safe combination written down on the slip of paper. The safe is in the room behind the counter. Inside there are many useful items
Artifact #40 - Hotel Keycard
After you start the generator and defeat the bloater in the flooded part of the hotel, go upstairs and find the security room.
On the table there is a keycard that you will need to open the door a bit further.
After Ellie saves you, climb up again and go left.
This way you will reach a broken staircase.
As you walk through the corridor below, you will pass by two toilets. In the second one, search through all of the stalls to find another pendant.