The patent application, which would still need to be approved and even then, may never reach production, describes tattooing, stamping or spraying "ferromagnetic" material into or onto a user's skin and then pairing it with a mobile device.
The device would need to be able to emit various magnetic fields. More than one type would be necessary so that the haptic tattoo or imprint could vibrate at varying intensities or patterns. The tattoo would also need to be "paired" with the device much as with headsets and BlueTooth devices, so that a phone call to your device doesn't set off everyone's tattoos.
The vibration pattern could also be different depending on who's calling, or it could differ depending on whether what the notification is for (email, SMS, calendar, etc.).
The filing said, "Examples of... applications may be low battery indication, received message, received call, calendar alert, change of profile, eg based on timing, change of time zone, or any other.
"The magnetic field may cause vibration of one short pulse, multiple short pulses, few long pulses... strong pulses, weak pulses and so on."
It doesn't have to be a tattoo; it could be something temporary like a stamp, patch or spray. If it were a tattoo, the ink would need to be demagnetized first. Then, after the tattoo is applied, it would be remagnetized by repeatedly running a powerful magnet over it.