The signature is just located directly under your posts on the forum and it's the place where you're allowed to advertise things, such as your Youtube series. If you look at the top right hand corner you should see an option that says "User CP", click that. The on the left hand side there will be a side bar titled "My Settings", look there and you'll see an option titled "Edit Signature". You can just throw a link in there if you want.
How you've gone about it is considered advertisement spam; you post the links with nothing really to add to the discussion. Whereas, if you had done what the OP did (i.e. posting the actual video and not a link to it, as well as a brief outline of your video and asking what people's thoughts/opinions were and if they agreed, what have you), there would be no problem. If you'd like to repost with the actual video instead of the link there is an "Insert Video" option located in the Quick Reply that looks like a film reel. If you do, please add something more to your post to go along with it though.
