This kind of stuff is so lame in campaigns. Sometimes it's from certain individuals that just hate all signs (as was the case with slicing of some of our Mark Strama signs last year). Other times it's childish pranksters. And opposing campaigns always hope it's not from their supporters, who can be impossible to control.
Given that that the name is cut out but the rest of the sign is still up, the pattern of attack seems more targeted at the candidate than the fact that it is a 4x8 in this case.