Here's one trick...
Brendan,
Enter the shoe late, just before the cut card is to be dealt, flat-betting until the shoe ends. As the dealer removes the undealt cards from the shoe and places them in the discard rack, notice exactly how high the stack is. For example, you might notice that the top of the decks is as high as the word "minimum" on the table limits sign.
Now, as long as you're sitting in that particular seat at that particular table, you can quickly estimate how many decks are in the discard rack. For example, if you look at the discards and notice that they're about halfway to the "minimum", then you know that half the decks (3 for a 6D shoe, 4 for an 8D shoe) are in the discard rack.
Hope this helps!
Dog Hand
