A bright red 'X'.
Jack skidded to a halt as he saw that tag on a piece of artwork. He stood, confused, dazed, almost. "I haven't seen that in a long time." he muttered to himself. He reached out to grab the piece of paper next to it. He studied it nor a moment, before he dashed away, leaving the paper for the next sprayer. As he strode across the rooftops, he slid his firearm into his hand, wary of a trap. When he worked as a Northgate guard, he knew that they were working on decoding it, but he was hopeful they hadn't made much progress.
As he arrived, peered into the building. It appeared to be something abandoned, possibly an apartment. He couldn't really see if there was anyone there. He quickly pulled up the bandana that covered his face, then flipped up his hood. He took a deep breath, then vaulted through a window, his gun raised. "Hello?" He said loudly, his voice echoing through the dusty lobby.
He almost shuddered with anticipation, having no idea whether or not he would be met by a Sprayer or officer. He slowly lowered the guns barrel a little bit, slowly reaching for his bag, to pull out a Molotov, in case someone called his bluff.