Speaking of restroom signs, I once found this website that posts series of unique restroom signs all over Japan.
(Sorry! The page is written only in Japanese, but I think its simple enough to look through!)
Here are some of the ones I thought it's interesting.
The silhouettes are drawn in an abstract form. Kind of like a brush stroke.
Is is just me, or do people especially like to personify cars?
I personally like these types of designs that use icons that represents the object and not the object itself. We can still easily understand the gender difference from the colors.
Wow, that's clever. The fishes are representing the directions as well.
Oh year, now that's really easy to understand.
Looking at the overall website, I noticed that even the shapes of the signs are greatly changed from silhouettes of man and woman, the blue and red (or black and red) colors compensate its understandability. Therefore, color is an important aspect of design.
However, still, signs that rely only on colors cannot be an universal design, since not all people can see colors accurately. The wall between functionality and creativity seems to be thicker than I think.