Love Mr. Froggy.
You should reposition the frog so it looks like he's climbing out the other side of the cubicle. If your boss mentions it, say, "Oh, really? I hadn't noticed."
A supervisor once stuck a silly photo high on the wall on my side of the office, where I didn't notice it for quite a while. Had to climb up on my desk to get it down. Of course, I then put it somewhere not very noticeable in his side. We went back and forth several times over the next few months, and then I forgot about it. At least a year later, I was promoted. When I took a framed poster off the wall to move it to my new office, I discovered the photo on the back!