Barrier Tag

These are special pieces of paper inscribed with the kanji for to "tie" or "bind" (結, ketsu), which is short for "barrier" (結界, kekkai). The tag most likely forms a barrier to protect whatever is located within it. When this tag was used, a shinobi was stationed above it, probably to maintain the technique.

Trivia
There was most likely several other tags and shinobi stationed around the area so as to complete the technique formation.