When you say the show is a couple of years old and the icon could be a spoiler, is the icon from something quite early on in the show, or is it something that's only very recently happened? I'd say if it was something from a couple of years ago, I wouldn't worry about it too much - as an example, this icon I have here is from a show about a similar age and it's from the first season. I don't worry too much about using this one - out of the people on my friends list who I know watch From, I know they've all got this far. I have held back on using one of a character who first appears part way through the most recent season though.

I've only seen bits of Torchwood, but I did know about Jack and Ianto, so I wouldn't think anything of that icon. Without having seen your other one from the show that's a couple of years old, or knowing what the show is, it's hard for me to judge how spoilery it is.