The Wanted poster is an artifact in the Left Behind DLC flashback chapter Mallrats, set in Boston. It lies on a table in an apartment Ellie and Riley pass through on their way to the mall.
A military poster seeking Marlene for Firefly affiliation, with front and side mugshots, her description and record, and a warning to civilians. On this copy someone has scrawled the word hero across the top.
Riley has just told Ellie she joined the Fireflies, so the defaced poster shows how some people in Boston see Marlene's group.
Warning note
The Warning note is an artifact in the Left Behind DLC flashback chapter Mallrats, set in Boston. It sits on a table in the room next to the circuit breakers Riley has Ellie flip to bring the mall's power back.
Boston Q.Z. Map
The Boston Q.Z. Map is the first artifact in the game and you cannot miss it: it is already inside Joel's backpack when you pick the bag up off a table in the smuggling tunnel during Beyond the Wall.
Davidson's Firefly Pendant
Davidson's Firefly pendant lies underwater in a stone rotunda in The Capitol Building section of The Outskirts. It belonged to Melinda Davidson and is easy to swim past.
Docks Note
The Docks Note is a gripe from one of Robert's smugglers, lying in the big warehouse at Mission Hill Pier where a fishing boat hangs over the loading bay. Look on the right side, against the railing behind a blue trash bin.