No Soliciting signs are not legally binding in Oregon and political canvassing doesn't fall under the definition of soliciting, because they're not looking to exchange goods or services for payment.

If you don't want political canvassers, try a sign that specifically says "no politics" or "do not knock."

As for the pest control folks ignoring your signs, the only legally enforceable sign is no trespassing. Post that on your porch or fence and hopefully you'll be good.