How does Johnny write a note to Ponyboy?

Johnny wrote Ponyboy a note in the dust of the floor with his finger.

"Johnny?" I called loudly, and that old wooden church echoed me, onny onny... I looked around wildly, almost panic-stricken, but then caught sight of some crooked lettering written in the dust of the floor. Went to get supplies. Be back soon. J.C.