Tracking labels required on every product for children under 13
http://www.cpsc.gov/about/cpsia/sect103policy.pdfMine says:
FayeMaloneDesigns.com
Kinsman, Oh, USA
Handemade in the USA
of Imported fabric
10ASONDJFMAMJJ11
The bottom numbers and letters coorespond to the years 2010, 2011 and the letters are the months of the year. I make a colored stitch under the year and month of completion of a garment. The label is sewn into the back of the garment along with size, and FTC tags.
For your blocks, you could have a brand made and brand one block. Use a wood burning tool to burn a dot under month and year. You could have a rubber stamp made, but you would have to have lead in paint testing results for your ink, and it would have to be permanant.