The combination of these two sign is often used in Rock and Roll culture. For most people, it represents the rebels sign. A negative impression, but like always, not everything is at it seems to be.
Lips, particularly female, are used often as an image to represent erogenous and intimate activity. Especially when pictured in a color or pattern associated with passion.
The sign of horns underneath the lips is an ancient way of expressing certain emotions. It is almost impossible to trace its origin but it dates back to Mediterranean culture. Where people used it as a protection against evil spirits or to curb bad luck. If somebody was confronted with bad events rock on gesture he used it to avoid the ill-fated and evil eye.