I don't believe you can embed the video itself in your signature, but you can definitely link to it.
As long as the link is under 200 characters and fits into the two lines. (assuming you dont have Toriprime)
And if it didn't fit that criteria you could always use a link shortener like *******
It's $10 USD, and it means you can use pictures (Amongst other things) in your sig, and change your user title. As you can see, magix has a title that says "FAG"