Last year my mother told me about a museum in London called The Foundling Museum and about an exhibition called Threads of Feeling. Here's an article about it from The Independent.
The babies who were abandoned at Thomas Coram's foundling hospital were registered with the mother's anonymity secured. The mothers left an identifying token, with the view that she might come back for the child. She left buttons, ribbon or a swatch of fabric.
The exhibition made available some of these swatches of fabric & documents created as the child was handed over.
You can see lots of photos of the exhibition via google images.
They are touching and poignant.
Also have a peak at the images/ comments in this bloghttp://www.somedaylondon.com/