this form of graffiti is very common thruout Oaktown aka Oakland. it's typical of the early days of "tagging"-spray painting upon public/private property without the owners' permission.
it's was primarily a moniker/handle or nom de plume of a virtual graffiti artist whose actual name is known only in the graffiti community ....here it's "SHOTZ". these are considered "noise".
or of a cartoon character (a head pic of a person with eyes staring leftward)...or "signature" cloud or bubble images or any other images.
the moniker graffiti(s) aren't appreciated by most viewers nor public officials and property owners. thus frequently whitewashed... the later is sometimes tolerated and allowed to be publicly displaced. read more