It's perhaps not an area we'd immediately associate with consent, but varying national laws can lead to confusion and distress when it comes to organ donation, which remains a contentious and emotionally charged issue.
This recent initiative out of Germany provides a free tattoo for those wishing to be organ donors.
As well as attracting attention and sparking conversation / awareness, the inking makes the wearer's wishes visible in situations where a relative's authorisation might otherwise be necessary.
According to its creators, Germany has one of the lowest organ donor rates in Europe, at 0.001%, and has no national register.
Some countries have an 'opt-out' system, whereby people's organs can be donated unless they have officially opted out; others such as Germany operate under the 'opt-in' system, in which people need to sign up / register / make their wishes formally known in order to donate organs.
The OPT-INK scheme, which turns a tattoo into a wearable consent form, was launched at a major tattoo festival and instantly generated long queues.
All it takes to opt-in to the explicit consent system is to carry proof of consent, whatever its form.
The actual design was created by a Berlin-based artist, Gara, and is designed to be easily recognised and re-created by a broad range of tattooists so as to boost scaleability.
Tattoo studios all over Germany are signing up for the scheme, and the Junge Helden organisation behind it provides a search facility for both tattooists and those wishing to receive the consent-wear.
Brilliant and much-needed concept / delivery; development open to harmful abuse; either or both, like most innovations?