Soundwave Tattoos are tattoos of audio in the shape of waveforms that can be scanned with the specially developed Skin Motion app and listened to. A description of the technology and process via the founder of Soundwave Tattoos, Nate Siggard while I see if 'Back Door Guests Are Best' looks like it would make a cool tramp stamp:

A person uploads or records the audio they want into the app or website. We generate the Soundwave from that. The person takes the generated Soundwave to a tattoo artist from our Artist Network. Artists need to be licensed in order to make sure they understand the limitations of the technology and how that applies to tattoo placement, size, and changes to the design of the tattoo from a simple Soundwave to make it more custom or elaborate on it for the person. Once the Artist does the tattoo, a photo of the tattoo is uploaded to our platform. Our platform processes the audio and tattoo and adds it to the app. When the user opens our app and points the camera on their mobile device at the tattoo, it recognizes the shape of the Soundwave and plays back the audio.

Sure, why not? Although they would be even cooler if the tattoos actually had a little audio player and speaker embedded beneath the skin so all you had to do was press them to play the audio. Plus if they were powered entirely by the blood pumping through your veins. What can I say, I'm a futurist. And speaking of blood pumping through my veins-- "You took too many boner pills?" Define too many. "More than one." Then yes, I took 6X too many.

Keep going for three video demonstrations, including one of a dog barking.

Thanks to lizzy, who agrees holographic tattoos are going to be the next real trend.