I'll respectfully disagree, because there are plenty of studies that show a wide gap in understanding of road signs, with some being considerably more intuitive to understand than others.

As an example, have a look at the data below:

As you can see, the "no powered vehicle" sign (red line through it) was understood by nearly everyone, with no confusion.

Compare that to the "no cycling", "no pedestrian" or "no motor vehicle" signs below:

You have mass confusion, with very few people actually knowing what the sign means before they are trained. To me, that's a design flaw.

Other studies show a similar pattern.

This one for example, asked people from different countries to identify the meaning of various traffic signs.

I will point out that the ones which scored nearly perfectly identified, are the ones with a line through them; Signs with just coloured circles were very often misidentified, or understood as having the opposite meaning.

We can go back and forth on this (I don't want to), and while I do agree that education can reduce the chance of a sign being misunderstood, that misses the point completely.