The reaction isn't exactly missed, per se. Bee knows his voice has some effect, but if it's a good one or a bad one is unknown at this point in time. Megatron giving him that look only confirms Bee's thoughts. Usually there's a smirk or some sort of smug expression. Right now? There's nothing.

It's almost creepy.

"That'd make one of us at least," comes the reply. "Kind of a surprise to me, you know?

His grin does falter the moment Megatron turns around. The badge... Well now he knows where his went. How could he not recognize it?