A "u" means it's unrated. "w" or "b" means that is the color that you play. If you start a game yourself and make yourself play White, you'll see a "w". I'm not sure about the warped pound sign or the vertical lines on a b.
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b = you play black
w = you play white
u = unrated
bu = you play black unrated
wu = you play white unrated
As for the other signs you're seeing, can you take a screenshot for me when you see them next please.
Computer Easy, Computer medium and Computer Hard were added yesterday morning (GMT time). Its like playing a rated version of little chess partner in live chess.
Because the seeks list can move so fast sometimes members click on the wrong seek so abort the game.
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