Graffiti has always existed as a form of expression amongst the people. Humor is often able to connect communities, sometimes even without the use of written language; who doesn’t like to laugh? Together, these tools can be used to tell subtle stories or express commonalities between individuals.
Highly visible, largely weatherproof, standardized, and easily interpretable canvases, such as road signs often find themselves vandalized in comical or political ways.
Sexual commentary or references to sexual actions are often an easy, but effective way to get a laugh from an audience. However some may find a piece like this to be distasteful. Road signs are widely viewed by people of all ages and backgrounds, and are meant to convey a message quickly and accurately. Graffiti on road signs can be considered harmful if the alteration to the sign is drastic enough, but that surely isn't the case with this sign.