THREE heavyset guys armed with aerosol canisters have their boombox tuned to a ribald talk-radio show as they transform a grungy section of wall in Long Island City, Queens, from a peeling mess to a psychedelic swirl of letters spelling out their names. The opposite of furtive, these tattooed artisans laugh as they brandish spraypaint cans for an audience of curious passers-by. Tagging may be illegal in New York, but not on this extraordinarily colorful industrial block beneath the shriek of the No. 7 subway line.