Territorial animals that we are, I'd add "here starts the territory of the Saber-Toothed Tiger Clan" signs to path markings as likely candidates for earliest symbolic communication.
Nice to see that the earliest examples of writing are still somewhat recognizable (as opposed to modern alphabets) - see https://en.wikipedia.org/wiki/History_of_writing - a hand, a foot, a goat or sheep.
Fun thing is, with modern technology we have regressed (advanced?) to a massive use of pictograms - a modern smartphone wielding human, in addition to the alphabet, knows at least a few hundreds or even thousands of pictograms ¯\_(ツ)_/¯