Also keep in mind that given the nature of a "recommendation" they are not a universal protection. Since they cannot be verified and are not uniform in style, they are often quite suspect. You can use the recommendation as an affirmative defense, but it may not prevent a seizure, cite or arrest (given the circumstances and the amount found in the vehicle). The assertiveness in enforcement varies by county.

If you want to have a proverbial "get out of jail card," then obtain the state-issued Medical Marijuana card. Absent that, you can be stopped and may find yourself cited.

As for DUI, that will depend upon the circumstances. One of the exceptions to the observed driving rule is if the officer can articulate a reasonable belief that you had been driving UI and "may cause injury to himself or herself or damage property unless immediately arrested." I'd be quite reluctant to leave a stoned driver alone in a vehicle.

If you smoke in your car, you pretty much guarantee a detention and a search on any and every traffic stop. That stuff reeks and gives probable cause for a search. So, if you enjoy police contact and an increased risk of citation and or arrest, keep it up. Otherwise, smoke your weed at home and transport it in the trunk of the car.