"A sign is either an icon, an index or a symbol... an index is a sign which would, at once, lose the character which makes it a sign if its object were removed." - Charles Sanders Peirce
The text itself - "If you reading this fuck you" - is pleasing and funny exactly because the "if" is so ineffective. By virtue of understanding the text, you almost certainly must be reading it. The resonance with the process of interpreting a QR code works similarly. If you've managed to resolve the code with your phone, the "if" clause has lost its meaning. Why involve an "if" clause? Why did the original artist not write "fuck you?"
In the context of street art, who knows? In the context of this collage, however, the layer of mediation puts an emphasis on the process of reading a work of art. The viewer must use a tool in order to resolve the meaning of the pasted-in code. In the case of a traditional collage, with an appropriated image or object, that tool is a mental infrastructure and cultural memory that makes it possible to resolve the identity of the appropriation. In the case of a QR code, that tool is a cellphone with a barcode app. A QR code, like a collage fragment, serves as something different than an icon or a symbol. QR codes is a concrete index, in the sense that Peirce defines index. That is, a QR code has an existential relationship to some link, text or phone number in the real world, just as a collage fragment is a chunk of reality, with a source in the real world, which has been taken out of context.
I chose to place the image in the front of a building because I didn't see any compelling reason to change the presentation mode of the original graffiti. QR codes are pointedly not web-specific - they're designed to be resolved on the street, by anybody walking by who wouldn't have time to copy down a complicated URL. Graffiti and QR codes are both ways of sending messages to passersby in the real world, so it seemed better to maintain the presentation format than to change it.
Finally, I was pleased to notice that a Google image search on my collage turns up the original photograph. Although I wouldn't expect a casual viewer to try that, I like the idea that both the QR code and the whole image can be resolved to their original referent through technology. I consider it an Easter Egg.