You can spot them pretty clearly as a bingo card is placed on the screen and the games are rendered against the cards as the slot reels are spinning. Some players have played them enough to be able to spot winning/losing patterns on the cards faster than the reels can render.
SLOTS LOBBY. You can only access slots from the bingo lobby itself. Switch to slots by going to the game menu (3 lines on the top right) and selecting Slots. Scroll horizontally to find a slots room you want to play in, then simply click it to open the room.