Yo g-t...look what I found......Google " TEXAS SCRATCHED INDIAN STONES "....Click about the 3rd listing
down...." GAULT SITE ENGRAVED STONES PAGE 1 "
Williamson Co. same as yours, a white limestone same as yours. Parallel lines like your snakes ( but no ladder rungs )...
These people have studied and offer possibilities for those "random scratches"
very interesting couple of pages to read.makes me think they used some sort of coloring pigment on those designs for transfer on skin or clothing. and being known to be mostly on paleo/clovis sites makes me think someone in that group is going to find the holy grail of artifacts.