A lot of the signs can be seen as symbols that are easy to draw with the hands. For example, there's the 5-dots and 6-dots symbols. Those are: "every finger of one hand" and "three fingers from each hand". The brush shapes are "bring all fingers together". There may very well be a communicative aspect to the symbols, but I think they were derived from decorative primitives that are kinesiologically-determined.
Possibly ad-hoc way finding, and reference points when lost, to help detect if you're going in circles, or if a change of direction is necessary.
If there are N number of confusing junctions, it would require the same number of markings as a unique mnemonic device to register the steps to escape the confusing area, and jog one's memory of how directions were negotiated the last time.
