Almost all European road signs are ideographic, for obvious reasons, much more so than US signs. And they are, of course, tested as part of licensing. There's

Almost all European road signs are ideographic, for obvious reasons, much more so than US signs. And they are, of course, tested as part of licensing. There's a design language you learn: circular for mandatory, triangular for advisory, square for informational. Blue background for positive, red border for negative.