has any variation of concentration ever used the minus sign to form a word like you see sometimes in print rebuses, such as (picture of a ski) - "S" = "key" or (picture of Oven) - (picture of Hen) to create "Of"?

I have watched a lot of all the versions of Concentration (NBC, Narz & Classic) and can say that I have never seen a minus sign used. I feel the reason it wasn't used was because you're trying to solve the puzzle with some boxes unexposed. Using the minus sign can muddy up the process. I feel you go in expecting the plus sign to be used but not the minus.

I have almost every home game, and it is not used there either.

To be fair, home games aren't always the best example to use when judging a games rules.

That said, I think Concentration was one of the best recreations, and of the editions I own (and of episodes I've seen), I never saw a minus sign either. I think the answer is no.

Only The Rebus Game used the minus.

Nope, minuses were not used in Concentration. I always thought it would be a good idea for a super endgame, like with a big prize or cash jackpot at stake, to include minuses.