I found a website that tells you what ribbon colors mean but unfortunately it doesn't say whether wearing a ribbon as a necklace means something different than wearing a ribbon as a lapel pin.
here's the site: http://www.causekeepers.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=C&Category_Code=Colors
Black Ribbon - 2013 was released on: USA: 21 August 2013
In the Aztec tradition, pregnant women wore a black ribbon, belt or sash to indicate their condition. Mary appears as the Virgin of Guadaluoe wearing the black ribbon.
A pink star alternated with a nautical black star stands for "Punk Rock Pink Ribbon", which symbolizes someone's battle with breast cancer. A pink star is an alternative to the pink ribbon. The nautical black star adds a 'punk rock' or 'alternative' spin to the pink star.
it mean
the black ribbon is in support of melanoma cancer patients.
Riddim Ribbon feat. The Black Eyed Peas happened in 2009.
Riddim Ribbon feat. The Black Eyed Peas was created in 2009.
The ribbon color for a fallen soldier is typically black to represent mourning and remembrance for those who have died in service.
Black Ribbon - 2007 was released on: USA: 28 September 2007 USA: 5 August 2008 (DVD premiere)
It could signify protection or a symbol of love and connection between you both. The black ribbon may have personal significance or cultural meaning in your relationship. It would be best to communicate with your wife to understand the reason behind this act.
A black ribbon (or wreath) on the front door of a home indicates someone has died.
If you wear a black ribbon it is usually to show that you are in mourning for someone. Often sports people will do this if a member of their team or someone closely associated with it has died.