It doesn't appear to be a stupid question at all. I just made one to try to find the answer to your question. I can't put it in an SDB, and when I place it, I can't put a price on it as I can with other furniture. So I have no idea if something changed since you bought yours or if you bought it by some other means, such as a trade, that you have forgotten about. Doubtless someone smarter than either of us will eventually enlighten us!
Well let's see, other than Wall segments, note poles are the only other furniture item that goes to your inventory. Remember when furniture was first released, wall segments were auctionable, but they had to recode furniture to allow it to be auctionable. Well maybe in the midst of all these furniture changes, they forgot to put the original code (like in the wall segments) into note poles.... I dunno, just a thought.
Nopers, I definitely got it out of a SDB. I remember, because I almost missed it -- they are so tall and skinny that when the graphic is sized down small enough to go on a SDB, it barely looks like anything.
And yep @Hawkwell -- I tried that too, but no dice.
I guess I'll just auction mine or stash them somewhere till I have a use for them. It just bugs me, because clearly it was possible not that long ago!