Whether or not additional examples of graffiti are actually the work of the same artist is a fact to be determined by a jury. What do you expect the prosecutor to do? Believe the defendant's word of honor, only after being caught red-handed?

Choosing to commit a crime that closely mimics the details of previous criminal activity by others (or yourself) is not the brightest idea. That is a kind stupidity that I am not sure we need special consideration for.