Reference for Maaser Sheni 5:1
כֶּרֶם רְבָעִי, מְצַיְּנִין אוֹתוֹ בְּקוֹזְזוֹת אֲדָמָה, וְשֶׁל עָרְלָה בְּחַרְסִית, וְשֶׁל קְבָרוֹת בְּסִיד, וּמְמַחֶה וְשׁוֹפֵךְ. אָמַר רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל, בַּמֶּה דְבָרִים אֲמוּרִים, בַּשְּׁבִיעִית. וְהַצְּנוּעִים מַנִּיחִין אֶת הַמָּעוֹת וְאוֹמְרִים, כָּל הַנִּלְקָט מִזֶּה, יְהֵא מְחֻלָּל עַל הַמָּעוֹת הָאֵלּוּ:
<i>Kerem Revai</i> [fruits in the fourth year after their planting, which are considered sacred], they mark it with clods of earth, and <i>Orlah</i> [fruits in the first three years after their planting, which may not be eaten] with pottery clay, and graves with lime, which he dissolves and pours. Rabban Shimon ben Gamaliel said: When does this apply? In the Sabbatical year. The conscientious put down coins and say: Any fruit gathered from this [vineyard] will be made into <i>Chulin</i> [non-sacred produce, by transferring their sacredness] to these coins.