Yes, there should definitely be a name for it. If expelling air through your lips while they are clenching your tongue (i.e. :-P) is called a “raspberry,” then the motion you described should at least be called something.
I know,.. well I didn’t know that, but I was finding it quite impossible to find a picture of someone doing this. You’d think it would be a semi standard smiley out there somewhere too,.....
@bagelface: Little kids do it all the time; they find it a wonderful and funny new discovery. I do too, as I am discovering right now. It sounds like Jeruba’s “wabba,” but from my lips to Fluther’s ear, it is more like “wubba,” or “bubbbawubba.”