From the Wikipedia page [1] which has images and references, and a discussion on the talk page:

The Gradeshnitsa tablets (Bulgarian language: Плочката от Градешница), unearthed in 1969 in north-western Bulgaria (Gradeshnitsa village, Vratsa Province), are, along with the Tărtăria tablets, an important testimony of late neolithic proto-writing known as the Vinča signs. The tablets are dated to the 5th millennium BC and are currently preserved in the Vratsa Archeological Museum of Bulgaria. In 2006, these tablets were the subject of attention in Bulgarian media due to claims made by Stephen Guide, a Bulgarian-American of the Institute of Transcendent Analysis, Long Beach, California, who claimed he had deciphered the tablets.

The Archaeology in Bulgaria page is [2].