Another old-timey meaning is "the horns of the cuckold," in other words, the person holding up the fingers is joking that the victim's spouse is adulterous. This "horns" business is prominent in Spain. When the Olympics were in Spain, and the US basketball "dream team" was full of Chicago Bulls, the marketers were surprised that Bulls gear sales did not jump in Spain. The reason was that the Bulls trademark would have marked the wearer as a guy whose wife was fooling around.
"You know what they say about sleeping dogs; you can't trust 'em." --Oliver Faltz