your sig is already 251px tall, 1px over the limit (!!!) so adding a spoiler to what you already have would make it far exceed the height limit, but if you use the small spoiler without a title, as jake has said above you might get away with it idk!!
In Jake's post, he says [ spoiler ] ( without spaces). What you want to do to name a spoiler is type in the name you want instead of spoiler. Example: [ spoiler=Pie is good ]( again, no spaces.)I hope this helped,if not I can explain it better