You definitely want to be careful about using upside down Rooks. It depends on which rules the tournament you are playing in follows:
FIDE - If the tournament is FIDE rated, even if played in the United States, they are obligated, no exceptions, to play under FIDE rules. FIDE rules state when it comes to promotion:
- If you push a pawn to the 8th rank (1st rank for Black), and hit the clock without making it anything, it's an illegal move, opponent gets 2 minutes unless it's the 2nd illegal move of the game by that player, in which case he forfeits the game, and it is then forced to be promoted to a Queen, regardless as to whether or not that creates a stalemate.
- "Declaring" a piece for the pawn is not "promoting" it. So pushing a7-a8 and saying "Knight", leaving it as a pawn there, and hitting the clock, is still an illegal move, and if it's White's first illegal move of the game, Black gets 2 minutes and it is automatically a Queen.
- Upside-down Rooks are Rooks! An upside-down Rook can never be used to represent a Queen. If no Queen is available, you must stop the clock, and ask the arbiter/director to find you a Queen. If you put an upside down Rook on the board, hit the clock, opponent moves, and then you move the upside down Rook diagonally, you just made an illegal move!
USCF - One thing I hate about USCF is that they have different rules than FIDE. When it comes to promotion, here's what's different about USCF vs FIDE:
- If you push a pawn to the 8th rank and not physically put a piece there, the opponent can hit the clock back without making a move, and the promoter is forced to put a piece there instead of a pawn. I once actually won on time because my opponent wouldn't physically put a new piece there, would leave it a pawn, and I just slapped the clock back at him without moving. The violator is not penalized via illegal move, and 2 minutes are not added to the opponent's clock, but again, the opponent is under no obligation to make a move, can hit the clock back at the first player, and is under no obligation to explain why he hit the clock back. It is the promoter's responsibility to figure out that he must place a piece there, and if his clock runs out, so be it!
- If you don't have a second Queen, you can use a Rook, placing it upside-down, to represent a Queen. An upside-down Rook can ONLY represent a Queen, NOT a third Knight or third Bishop. If you need a third knight, you must stop the clock to get a director to find you a Knight of whatever color you are playing as.
Most sets do now.