I'm sure this is staring me in the face somewhere but I'm darned if I can find it.

Where is some information about when and what links we can leave in our posts?

I haven't had it happen to me yet, but I've seen quite a few posts lately which have had links to sites removed, often when I've needed the link to respond to the question being asked and I'm not sure why they've been removed. Sometimes it's obvious why links have been removed, but lately I've noticed lots of links from what look like genuine posters (not spam) being removed as well hence the question. I'd rather not land myself in trouble for posting links when I'm not allowed, I've already got in trouble for something else recently :P Incidentally, this is the only forum I've ever got into trouble on, so I'm a little paranoid round here now!