Miles is a graffiti artist
We can see this in the first minutes of the movie when he is doodling in these name tag stickers and putting them around the neighborhood, this pisses off his dad because he is a police officer and graffiti is illegal in New York.
Miles is also a kid, who doesn't have money and permission to buy real paint to paint real graffiti, that's why he uses these stickers.
This is paid off later when uncle Aron takes Miles to a place to paint a full mural with real spray paint.
And also as @OrageDog pointed out, Sticker art is a form of street art:
Sticker art (also known as sticker bombing, sticker slapping, slap tagging, and sticker tagging) is a form of street art in which an image or message is publicly displayed using stickers. These stickers may promote a political agenda, comment on a policy or issue, or comprise a subcategory of graffiti.