From the Norfolk City Code of Ordinances:



Sec. 27-41. - Purpose and intent.

It is the purpose and intent of this chapter to provide a procedure for removal of graffiti from walls and structures on both public and privately owned property in order to reduce blight and deterioration within the city and to protect the public safety, and to provide for the recovery of costs of such removal, and to provide a measure of rehabilitation, through community service, for those persons guilty of violations of this chapter.

Sec. 27-42. - Graffiti declared a nuisance.

The existence of graffiti within the city limits of the City of Norfolk, Virginia, as defined below, is declared by this council to be obnoxious and a public and private nuisance and must be quickly abated to avoid the detrimental impact of such graffiti on the city and its residents, and to prevent the further spread of such graffiti.

Sec. 27-43. - Definitions.

As used in this article, "graffiti" includes but shall not be limited to any non-permitted inscription, word, figure, or design that is marked, etched, scratched, drawn, painted, pasted or otherwise affixed to, or on, any sidewalk, wall, building, fence, pole, sign, utility cabinet, or any other structure or surface, regardless of the nature of the material of that structural component. 
As used in this article, "person" means any individual, firm, owner, sole proprietorship, corporation, unincorporated association, governmental body, municipal corporation, executor, administrator, trustee, guardian, agent, occupant or other legal entity. 

Sec. 27-44. - Graffiti prohibited.

It shall be unlawful and a class 1 misdemeanor for any person to apply graffiti on any surface or structure within the city.



According to the City Code, graffiti is graffiti, no matter how it is affixed to a structure or surface (and that includes locking it to it with a padlock). So a padlock bearing an inscription (traditional graffiti), is the means by which that graffiti is attached to the bridge:


As for the many padlocks on the bridge that bear no inscription, figure, design, or anything else, they, too, qualify as a type of graffiti. Consider, for example, yarn bombing. This type of graffiti is the practice of covering a structure with knitted yarn, and it, too, requires no inscriptions, figures, etc. Think lock bombing.

By the way, yarn bombing even started appearing on the Hague bridge once — no doubt inspired by the lock graffiti. But since the yarn bombing wasn't locked to the bridge like the padlocks, it soon disappeared: