Some Tattoos Found to Interfere With Apple Watch's Sensors
A growing number of users have turned to social networks claiming that full sleeve tattoos, ones that stretch to cover the wrist, interfere with the Apple Watch's heart rate sensor and skin contact registration. Consequently, some Apple Watch users with tattoos have been unable to receive notifications and are frequently prompted to re-enter their passcode, if one is set, on the wrist-worn device.
A popular Reddit thread discussing the issue has received nearly 700 upvotes and 300 comments since being posted on Tuesday, and some users have unfortunately already coined the phrase "Tattoogate" to describe the problem. More soon followed up with a report confirming the issue, with the Apple Watch displaying inaccurate heart rate readings on the wrists of people with dark-colored tattoos.
http://www.macrumors.com/2015/04/29/apple-watch-sensors-tattoogate/
In this day and age, hard to imagine they didn't factor inked skin into their testing.
= new reply since forum marked as read
Maybe clear in the shape of the Apple logo. Problem solved. 
