I find it suspicious that the set of the most common symbols doesn't contain a dick. Why wouldn't the most common modern wall ornament (in my experience) be popular at that time?
In the tomb of Ti at Saqqara, in a mural depicting a battle, there is a hieroglyph comprising a stylised phallus entering an even more stylised vulva. It is an insult that one warrior is hurling at his enemy. Apparently it is usually translated, somewhat primly, as "Come here, you copulator"; in his Scorn: With Added Vitriol (a collection of invective across the ages), Matthew Parris prefers the earthier "Come 'ere, you fucker."
While the symbol may not be very useful for telling stories I think it should still be pretty common because it could be used for "artistic expression", demonstration of dominance, a joke or vandalism.
