Odd Language #201: No Passing

A British Columbia road sign I have seen many times: “DO NOT PASS SNOWPLOWS ON RIGHT”

The issue: Due to elision of words to fit, it is ambiguous. Does it mean to not pass snowplows that are on one’s right or to not pass snowplows on their right? Actually, neither is a particularly good idea, but it is the latter. Where do you think they throw their snow?