Signs are conceptual expressions that are impossible to find in real life but are repeated expressions of a certain pattern .
Some have signs with certain patterns , but it is hard to classify them on the basis of engravings on the rock alone .
Signs are conceptual signs that are impossible to find in real life but are repeated expressions of a certain pattern .
Some have signs with certain patterns , but it is hard to classify them on the basis of engravings on the rock alone .