Duck and Cover! underneath the bed in Dean Domino's room. Can only be coaxed out using grenades. Extremely difficult.
There are three Lover's mark stash locations. The first is just to the left as you enter the area from the Villa containing miscellaneous foodstuffs. The second is south of the stairs leading to Domino's room, in the SW corner of the courtyard, behind the corner arch pillar, and has ammo, and the third is up the second set of stairs next to the cloud covered courtyard with the tripwire and grenade trap. Next to the stove in the corner.
Ace of Diamonds - Sierra Madre: Around the corner southwest of the door to the Villa, past a vending machine and tree stump, under the south end of a bench.
2 of Spades - Sierra Madre: Inside a second floor room with a pressure plate, rigged shotgun and fire extinguisher trap, with cloud covered courtyards to the south and (along with two dead trees and three tree stumps) to the east, behind a bed against the north wall.
7 of Hearts - Sierra Madre: Inside a second floor room with a tripwire and rigged shotgun, southeast of the doors to the Villa and east of the wall fountain and stairs seen when entering, on a wooden coffee table with two bottles of dirty water.