My shoelaces cross over each other four times in each shoe. Using the different directions of crossing, that's eight undetectable bits. You can do a lot with eight bits.

But read subltle differences in shoe-lace patterns after a glance and cross-reference with the list of meanings? Hard. They'd just look like a mess to me. I suspect that the most you can get out of it reliably is about 2 bits, so four signals, including one zero state meaning "no message".

That's what training is for. To the untrained eye it may seem hard to distinguish.