Dreams Don't Die. 1982

Plot line :
Two young kids in love, one young graffiti artist and the other a foster-child, find trouble on the mean streets on the other side of the river in New York City. Officer Charles Banks finds young Danny tagging subway cars and then catches Teiresa selling drugs for another mislead teen, Kirk. The officer, instead of turning both of them in, gives both teens a chance blah blah blah.
Well cheesy but it's got old graffiti, on trains and everything! Done by Dondi apparently. 
Thanks 2 Teach for the link