Would it be considered obstruction of justice to use a sign to warn drivers of a speed trap?

The reason I ask is because there is a speed trap about a block from my house every week. The cops that man it are incredibly rude and unforgiving. They catch upwards of about 90% of the traffic because the speed was recently reduced from 25mph to 18mph. If I made a sign and sat on the sidewalk a block or so away to warn people to slow down would I get in trouble?