Unless that's a private drive, the roadside where the crosses are is likely a county right of way. No trespassing, and unless those signs complied with applicable signage regulations, no vandalism, either.
Maybe reckless driving, though the driver could say all the crosses made him begin to weep, blurring his vision of the roadway.
Whoa. You said what I said, only I hadn't gotten to yours when I said what I said!